LT1715CMS [Linear]

4ns, 150MHz Dual Comparator with Independent Input/Output Supplies; 为4ns , 150MHz的双通道比较器,带有独立的输入/输出电源
LT1715CMS
型号: LT1715CMS
厂家: Linear    Linear
描述:

4ns, 150MHz Dual Comparator with Independent Input/Output Supplies
为4ns , 150MHz的双通道比较器,带有独立的输入/输出电源

比较器 放大器 光电二极管
文件: 总16页 (文件大小:243K)
中文:  中文翻译
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LT1715  
4ns, 150MHz  
Dual Comparator with  
Independent Input/Output Supplies  
U
FEATURES  
DESCRIPTIO  
The LT®1715 is an UltraFastTM dual comparator optimized  
for low voltage operation. Separate supplies allow inde-  
UltraFast: 4ns at 20mV Overdrive  
150MHz Toggle Frequency  
Separate Input and Output Power Supplies  
Low Power: 4.6mA per Comparator at 3V  
Pinout Optimized for High Speed Use  
Output Optimized for 3V and 5V Supplies  
TTL/CMOS Compatible Rail-to-Rail Output  
Input Voltage Range Extends 100mV  
Below Negative Rail  
pendent analog input ranges and output logic levels with  
no loss of performance. The input voltage range extends  
from100mVbelowVEE to1.2VbelowVCC. Internalhyster-  
esis makes the LT1715 easy to use even with slow moving  
input signals. The rail-to-rail outputs directly interface to  
TTL and CMOS. The symmetric output drive results in  
similar rise and fall times that can be harnessed for analog  
applications or for easy translation to other single supply  
logic levels.  
Internal Hysteresis with Specified Limits  
U
The LT1715 is available in the 10-pin MSOP package. The  
pinout of the LT1715 minimizes parasitic effects by plac-  
ing the most sensitive inputs away from the outputs,  
shielded by the power rails.  
APPLICATIO S  
High Speed Differential Line Receivers  
Level Translators  
Window Comparators  
Crystal Oscillator Circuits  
Threshold Detectors/Discriminators  
High Speed Sampling Circuits  
Delay Lines  
For a dual/quad single supply comparator with similar  
propagation delay, see the LT1720/LT1721. For a single  
comparatorwithsimilarpropagationdelay,seetheLT1719.  
, LTC and LT are registered trademarks of Linear Technology Corporation.  
UltraFast is a trademark of Linear Technology Corporation.  
U
TYPICAL APPLICATIO  
100MHz Dual Differential Line Receiver  
Line Receiver Response to 100MHz Clock,  
50MHz Data Both with 25mVP-P Inputs  
5V  
3V  
3V  
+
CLOCK OUT  
1V/DIV  
OUT A  
OUT B  
IN A  
IN B  
0V  
3V  
DATA OUT  
0V  
1V/DIV  
+
FET PROBES  
5ns/DIV  
1715 TA02  
1715 TA01  
–5V  
1
LT1715  
W W U W  
U W  
U
ABSOLUTE AXI U RATI GS  
PACKAGE/ORDER I FOR ATIO  
(Note 1)  
ORDER PART  
NUMBER  
Supply Voltage  
+VS to GND .......................................................... 7V  
V
CC to VEE........................................................ 13.2V  
TOP VIEW  
LT1715CMS  
LT1715IMS  
+IN A  
–IN A  
–IN B  
+IN B  
1
2
3
4
5
10  
9
V
CC  
S
OUT A  
OUT B  
GND  
+VS to VEE ....................................................... 13.2V  
VEE to GND ....................................... 13.2V to 0.3V  
Input Current (+IN, IN) ................................... ±10mA  
Output Current (Continuous) ............................ ±20mA  
Operating Temperature Range ................ 40°C to 85°C  
Specified Temperature Range (Note 2)... 40°C to 85°C  
Junction Temperature.......................................... 150°C  
Storage Temperature Range ................ 65°C to 150°C  
Lead Temperature (Soldering, 10 sec)................. 300°C  
A
+V  
8
7
6
B
V
EE  
MS10 PACKAGE  
10-LEAD PLASTIC MSOP  
MS10 PART MARKING  
TJMAX = 150°C, θJA = 120°C/ W (NOTE 3)  
LTVQ  
LTVV  
Consult factory for parts specified with wider operating temperature ranges.  
ELECTRICAL CHARACTERISTICS  
The denotes specifications that apply over the full operating temperature  
range, otherwise specifications are at TA = 25°C. VCC = 5V, VEE = –5V, +VS = 5V, VCM = 1V, COUT = 10pF, VOVERDRIVE = 20mV,  
unless otherwise specified.  
SYMBOL  
– V  
PARAMETER  
CONDITIONS  
MIN  
2.7  
TYP  
MAX  
12  
UNITS  
V
Input Supply Voltage  
Output Supply Voltage  
Input Voltage Range  
Input Trip Points  
V
V
V
CC  
EE  
+V  
2.7  
6
S
V
(Note 4)  
(Note 5)  
V
– 0.1  
V
– 1.2  
CC  
CMR  
EE  
+
V
V
1.5  
5.5  
5.5  
1.5  
mV  
mV  
TRIP  
TRIP  
V
Input Offset Voltage  
(Note 5)  
(Note 5)  
0.4  
2.5  
3.5  
mV  
mV  
OS  
V
Input Hysteresis Voltage  
Input Offset Voltage Drift  
Input Bias Current  
2
3.5  
10  
6
mV  
µV/°C  
µA  
HYST  
V /T  
OS  
I
I
–6  
–2.5  
0.2  
70  
0
B
Input Offset Current  
0.6  
µA  
OS  
CMRR  
PSRR  
Common Mode Rejection Ratio  
Power Supply Rejection Ratio  
Voltage Gain  
(Note 6)  
(Note 7)  
(Note 8)  
60  
65  
dB  
80  
dB  
A
V
V
V
+
Output High Voltage  
I
I
= 4mA, V = V  
+ 20mV  
+V – 0.4  
V
V
OH  
SOURCE  
IN  
TRIP  
S
Output Low Voltage  
= 10mA, V = V  
– 20mV  
0.4  
OL  
SINK  
IN  
TRIP  
f
t
Maximum Toggle Frequency  
Propagation Delay  
(Note 9)  
150  
4
MHz  
MAX  
PD20  
V
V
= 20mV (Note 10),  
EE  
2.8  
2.8  
6
7
ns  
ns  
OVERDRIVE  
CC  
= 5V, V = –5V  
V
V
= 20mV, V = 5V, V = 0V  
4.4  
4.8  
ns  
OVERDRIVE  
OVERDRIVE  
CC  
EE  
= 20mV, V = 3V, V = 0V  
3
3
6.5  
7.5  
ns  
ns  
CC  
EE  
t
t
Propagation Delay  
V
= 5mV, V = 0V (Notes 10, 11)  
6
9
12  
ns  
ns  
PD5  
OVERDRIVE  
EE  
+
Propagation Delay Skew  
(Note 12) Between t /t , V = 0V  
0.5  
1.5  
ns  
SKEW  
PD PD  
EE  
2
LT1715  
ELECTRICAL CHARACTERISTICS  
unless otherwise specified.  
The denotes specifications that apply over the full operating temperature  
range, otherwise specifications are at TA = 25°C. VCC = 5V, VEE = –5V, +VS = 5V, VCM = 1V, COUT = 10pF, VOVERDRIVE = 20mV,  
SYMBOL  
t  
PARAMETER  
CONDITIONS  
MIN  
TYP  
0.3  
2
MAX  
UNITS  
ns  
Differential Propagation Delay  
Output Rise Time  
(Note 13) Between Channels  
10% to 90%  
1
PD  
t
t
t
ns  
r
f
Output Fall Time  
90% to 10%  
2
ns  
+
Output Timing Jitter  
V
= 1.2V (6dBm), Z = 50Ω  
t
15  
11  
ps  
RMS  
ps  
RMS  
JITTER  
IN  
P-P  
IN  
PD  
PD  
f = 20MHz (Note 14)  
t
I
I
I
Positive Input Stage Supply Current  
(per Comparator)  
+V = V = 5V, V = 5V  
1
2
mA  
mA  
mA  
mA  
mA  
mA  
CC  
S
CC  
EE  
+V = V = 3V, V = 0V  
0.9  
1.6  
S
CC  
EE  
Negative Input Stage Supply Current  
(per Comparator)  
+V = V = 5V, V = 5V  
4.8  
3.8  
2.9  
2.4  
4.6  
EE  
S
S
CC  
EE  
+V = V = 3V, V = 0V  
S
CC  
EE  
Positive Output Stage Supply Current  
(per Comparator)  
+V = V = 5V, V = 5V  
7.5  
6
S
CC  
EE  
V = V = 3V, V = 0V  
3.7  
S
CC  
EE  
Note 1: Absolute Maximum Ratings are those values beyond which the life  
of a device may be impaired.  
Note 8: Because of internal hysteresis, there is no small-signal region in  
which to measure gain. Proper operation of internal circuity is ensured by  
measuring V and V with only 20mV of overdrive.  
OH  
OL  
Note 2: The LT1715C is guaranteed to meet specified performance from  
0°C to 70°C. The LT1715C is designed, characterized and expected to  
meet specified performance from –40°C to 85°C but is not tested or QA  
sampled at these temperatures. The LT1715I is guaranteed to meet  
specified performance from –40°C to 85°C.  
Note 9: Maximum toggle rate is defined as the highest frequency at which  
a 100mV sinusoidal input results in an error free output toggling to greater  
than 4V when high and to less than 1V when low on a 5V output supply.  
Note 10: Propagation delay measurements made with 100mV steps.  
±
Note 3: Thermal resistances vary depending upon the amount of PC board  
Overdrive is measured relative to V  
.
TRIP  
2
metal attached to Pin 5 of the device. θ is specified for a 2500mm 3/32"  
JA  
Note 11: t cannot be measured in automatic handling equipment with  
PD  
2
FR-4 board covered with 2oz copper on both sides and with 100mm of  
low values of overdrive. The LT1715 is 100% tested with a 100mV step  
and 20mV overdrive. Correlation tests have shown that t limits can be  
guaranteed with this test.  
Note 12: Propagation Delay Skew is defined as:  
copper attached to Pin 5. Thermal performance can be improved beyond  
the given specification by using a 4-layer board or by attaching more metal  
area to Pin 5.  
Note 4: If one input is within these common mode limits, the other input  
can go outside the common mode limits and the output will be valid.  
PD  
t
= |t  
– t  
|
PDHL  
SKEW  
PDLH  
Note 13: Differential propagation delay is defined as the larger of the two:  
Note 5: The LT1715 comparator includes internal hysteresis. The trip  
t  
PDLH  
t  
PDHL  
= |t  
= |t  
– t  
PDLHB  
– t  
PDHLB  
|
|
PDLHA  
PDHLA  
points are the input voltage needed to change the output state in each  
+
direction. The offset voltage is defined as the average of V  
while the hysteresis voltage is the difference of these two.  
and V  
,
TRIP  
TRIP  
Note 14: Package inductances combined with asynchronous activity on  
the other channel can increase the output jitter. See Channel Interactions  
in Applications Information. Specification above is with one channel active  
only.  
Note 6: The common mode rejection ratio is measured with V = 5V,  
CC  
V
V
= 5V and is defined as the change in offset voltage measured from  
EE  
= 5.1V to V = 3.8V, divided by 8.9V.  
CM  
CM  
Note 7: The power supply rejection ratio is measured with V = 1V and is  
CM  
defined as the worst of: the change in offset voltage from V = +V =  
CC  
S
2.7V to V = +V = 6V (with V = 0V) divided by 3.3V or the change in  
CC  
S
EE  
offset voltage from V = 0V to V = 6V (with V = +V = 6V) divided  
EE  
EE  
CC  
S
by 6V.  
3
LT1715  
TYPICAL PERFOR A CE CHARACTERISTICS  
U W  
Input Offset and Trip Voltages  
vs Supply Voltage  
Input Offset and Trip Voltages  
vs Temperature  
Input Common Mode Limits  
vs Temperature  
3
2
3
2
4.2  
4.0  
+V = V = 5V  
+
S CC  
= 1V  
CM  
= –5V  
EE  
+V = V = 5V  
S
EE  
CC  
= 5V  
V
TRIP  
V
V
V
+
V
TRIP  
3.8  
3.6  
1
0
1
V
OS  
V
OS  
0
4.8  
5.0  
5.2  
–1  
–2  
–3  
–1  
–2  
–3  
V
TRIP  
V
TRIP  
T
V
V
= 25°C  
A
= 1V  
CM  
= GND  
EE  
5.4  
60 40 20  
0
20 40 60 80 100 120 140  
4.5  
5.5 6.0  
50  
TEMPERATURE (°C)  
100 125  
2.5 3.0  
3.5 4.0  
5.0  
50 25  
0
25  
75  
TEMPERATURE (°C)  
SUPPLY VOLTAGE, V = +V (V)  
CC  
S
1715 G02  
1715 G01  
1715 G03  
Input Current  
vs Differential Input Voltage  
Quiescent Supply Current  
vs Temperature  
Quiescent Supply Current  
vs Supply Voltage  
2
1
6
5
8
6
V
CC  
V
EE  
= +V = 5V  
S
= –5V  
T
= 25°C  
EE  
T
V
V
= 25°C  
A
A
I , OUTPUT HIGH  
S
V
= GND  
= +V = 5V  
CC  
S
= –5V  
EE  
4
0
I
S
4
3
I , OUTPUT LOW  
S
–1  
–2  
–3  
–4  
–5  
–6  
–7  
2
2
I
CC  
1
I
CC  
0
0
–1  
–2  
–3  
–4  
–2  
–4  
–6  
I
, OUTPUT LOW  
EE  
I
EE  
I
EE  
, OUTPUT HIGH  
25  
0
50  
75 100 125  
4
7
–5 –4 –3 –2 1  
0
5
50  
25  
0
2
3
5
6
1
2
3
4
1
DIFFERENTIAL INPUT VOLTAGE (V)  
SUPPLY VOLTAGE, V = +V (V)  
TEMPERATURE (°C)  
CC  
S
1715 G04  
1715 G05  
1715 G06  
Output Low Voltage  
vs Load Current  
Output High Voltage  
vs Load Current  
Supply Current  
vs Toggle Frequency  
–0.1  
–0.2  
–0.3  
–0.4  
–0.5  
–0.6  
0.5  
0.4  
0.3  
0.2  
0.1  
0
30  
25  
VALID  
TOGGLING  
INCOMPLETE  
OUTPUT TOGGLING  
V
= +V = 5V, UNLESS  
V
= +V = 5V, UNLESS  
CC S  
CC  
S
125°C  
OTHERWISE NOTED  
OTHERWISE NOTED  
+V = 2.7V  
S
V
= –10mV  
V
= 10mV  
IN  
IN  
125°C  
C
LOAD  
= 20pF  
C
= 10pF  
LOAD  
55°C  
20  
55°C  
25°C  
15  
10  
25°C  
C
LOAD  
= 0pF  
125°C  
T
= 25°C  
IN  
A
V
= ±50mV SINUSOID  
5
0
125°C  
+V = 2.7V  
+V = V = 5V  
V
S
EE  
CC  
= GND  
S
0
4
8
12  
16  
20  
0
4
8
12  
16  
20  
175  
200 225  
0
25 50 75 100 125 150  
OUTPUT SOURCE CURRENT (mA)  
TOGGLE FREQUENCY (MHz)  
OUTPUT SINK CURRENT (mA)  
1715 G08  
1715 G07  
1715 G09  
4
LT1715  
U W  
TYPICAL PERFOR A CE CHARACTERISTICS  
Propagation Delay  
vs Overdrive  
Propagation Delay  
vs Temperature  
Propagation Delay  
vs Supply Voltage  
8.0  
7.5  
7.0  
6.5  
6.0  
5.5  
5.0  
4.5  
4.0  
3.5  
3.0  
5.5  
5.0  
4.5  
4.0  
3.5  
8
7
6
5
4
3
t
C
= 10pF  
T
V
C
= 25°C  
PDLH  
STEP  
LOAD  
T
= 25°C  
STEP  
A
A
V
V
= 100mV  
= 100mV  
= 100mV  
STEP  
LOAD  
= 10pF  
OVERDRIVE = 20mV  
C
= 10pF  
LOAD  
V
V
= +V = 3V  
S
CC  
EE  
= 0V  
V
CC  
V
= +V = 3V  
EE  
OVERDRIVE = 5mV  
S
t
PDLH  
= 0V  
V
= GND  
EE  
t
PDHL  
t
t
PDLH  
t
PDLH  
PDHL  
t
PDLH  
t
PDHL  
V
EE  
= –5V  
V
CC  
V
= +V = 5V  
EE  
V
= +V = 5V  
S
S
CC  
OVERDRIVE = 20mV  
= –5V  
V
= –5V  
t
EE  
PDHL  
10  
20  
OVERDRIVE (mV)  
40  
25  
0
50  
75 100 125  
4.5  
5.5  
+
6.0  
0
50  
50  
25  
2.5 3.0  
3.5 4.0  
5.0  
30  
TEMPERATURE (°C)  
SUPPLY VOLTAGE, +V = V OR V (V)  
S
CC  
1715 G10  
1715 G11  
1715 G12  
Maximum Toggle Rate  
vs Input Amplitude  
Maximum Toggle Rate  
vs Temperature  
Maximum Toggle Rate  
vs Supply Voltage  
250  
230  
210  
190  
170  
150  
130  
110  
90  
180  
250  
225  
200  
175  
150  
125  
100  
75  
T
= 25°C  
T
= 25°C  
A
A
TOGGLING FROM  
+V = V = 5V  
V = ±50mV SINUSOID  
160  
140  
120  
100  
80  
S
EE  
CC  
IN  
1V TO +V – 1V  
V
C
= GND  
+V = V = 5V  
S
S
EE  
LOAD  
LOAD  
CC  
= 10pF  
V
C
R
= –5V  
LOAD  
= 10pF  
= 500Ω  
TOGGLING FROM  
20% TO 80% OF +V  
S
60  
T
= 25°C  
40  
A
V
= ±50mV SINUSOID  
IN  
EE  
20  
V
C
= GND  
= 10pF  
70  
LOAD  
0
50  
50  
1
10  
INPUT SINUSOID AMPLITUDE (mV)  
100  
–50  
0
25  
50  
75  
125  
–25  
100  
4
2
3
5
6
TEMPERATURE (°C)  
+V = V SUPPLY VOLTAGE (V)  
S
CC  
1715 G13  
1715 G14  
1715 G15  
Maximum Toggle Rate  
vs Load Capacitance  
Propagation Delay  
Response to 150MHz 25mVP-P  
Sine Wave Driving 10pF  
vs Load Capacitance  
250  
225  
200  
175  
150  
125  
100  
75  
8
7
6
5
4
3
NA  
T
= 25°C  
IN  
T
= 25°C  
STEP  
A
A
25mVP-P  
20mV/DIV  
1V/DIV  
V
= ±50mV SINUSOID  
V
= 100mV  
+V = V = 5V  
V
OVERDRIVE = 20mV  
+V = V = 5V  
S
EE  
CC  
= GND  
5V  
S
EE  
CC  
= –5V  
V
OUT A  
0V  
RISING EDGE  
(t  
)
PDLH  
FALLING EDGE  
(t  
)
PDHL  
FET PROBES  
VCC = 5V  
2.5ns/DIV  
1715 G18  
V
EE = –5V  
50  
+VS = 5V  
VCM = 0V  
10  
20  
40  
0
5
10 15 20 25 30 35 40 45 50  
OUTPUT CAPACITANCE (pF)  
1715 G16  
0
50  
30  
OUTPUT LOAD CAPACITANCE (pF)  
1715 G17  
5
LT1715  
U
U
U
PI FU CTIO S  
+IN A (Pin 1): Noninverting Input of Comparator A.  
IN A (Pin 2): Inverting Input of Comparator A.  
IN B (Pin 3): Inverting Input of Comparator B.  
+IN B (Pin 4): Noninverting Input of Comparator B.  
GND (Pin 6): Ground for Output Stage.  
OUT B (Pin 7): Output of Comparator B.  
OUT A (Pin 8): Output of Comparator A.  
+VS (Pin 9): Positive Supply Voltage for Output Stage.  
V
EE (Pin 5): Negative Supply Voltage for Input Stage and  
V
CC (Pin 10): Positive Supply Voltage for Input Stage.  
Substrate.  
TEST CIRCUITS  
±VTRIP Test Circuit  
LTC203  
BANDWIDTH-LIMITED TRIANGLE WAVE  
1kHz, V ±7.5V  
~
CM  
14  
15  
3
2
V
CC  
+
0.1µF  
1000 × V  
TRIP  
50k  
1µF  
10nF  
10k  
+
16  
9
1
8
DUT  
50Ω  
1/2 LT1715  
50Ω  
1/2 LT1112  
200k  
1000 × V  
HYST  
+
V
CM  
11  
10  
6
7
1000 × V  
OS  
10k  
LTC203  
3
2
14  
15  
1/2 LT1638  
+
1000 × V  
TRIP  
100k  
100k  
1µF  
10nF  
1
8
16  
9
+
2.4k  
100k  
100k  
1/2 LT1638  
1/2 LT1112  
+
0.15µF  
6
7
11  
10  
1715 TC01  
NOTES: LT1638, LT1112, LTC203s ARE POWERED FROM ±15V.  
200kPULL-DOWN PROTECTS LTC203 LOGIC INPUTS  
WHEN DUT IS NOT POWERED  
6
LT1715  
TEST CIRCUITS  
Response Time Test Circuit  
+V – V  
s
CM  
0V  
0.01µF  
0.01µF  
V
– V  
CM  
CC  
–100mV  
25Ω  
+
DUT  
1/2 LT1715  
10× SCOPE PROBE  
25Ω  
(C 10pF)  
50k  
IN  
0.1µF  
130Ω  
50Ω  
V1*  
PULSE  
IN  
2N3866  
0V  
V
– V  
1N5711  
EE  
CM  
–3V  
–V  
+
CM  
50Ω  
400Ω  
750Ω  
*V1 = –1000 • (OVERDRIVE + V  
)
TRIP  
NOTE: RISING EDGE TEST SHOWN.  
1715 TC02  
FOR FALLING EDGE, REVERSE LT1719 INPUTS  
–5V  
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2.7V TO 6V  
Power Supply Configurations  
5V  
The LT1715 has separate supply pins for the input and  
output stages that allow flexible operation, accommodat-  
ing separate voltage ranges for the analog input and the  
outputlogic.Ofcourse,asingle3V/5Vsupplymaybeused  
by tying +VS and VCC together as well as GND and VEE.  
V
V
CC  
CC  
EE  
3V  
+V  
+
+
+V  
S
S
GND  
GND  
V
V
EE  
5V  
Theminimumvoltagerequirementcanbesimplystatedas  
boththeoutputandtheinputstagesneedatleast2.7Vand  
the VEE pin must be equal to or less than ground.  
Single Supply  
±5V Input, 3V Output Supplies  
12V  
The following rules must be adhered to in any  
configuration:  
V
V
CC  
CC  
5V  
+V  
3V  
+V  
+
+
S
S
2.7V (VCC – VEE) 12V  
2.7V (+VS – GND) 6V  
(+VS – VEE) 12V  
GND  
GND  
V
V
EE  
EE  
5.2V  
1715 F01  
V
EE Ground  
12V Input, 5V Output Supplies Front End Entirely Negative  
Although the ground pin need not be tied to system  
ground, most applications will use it that way. Figure 1  
shows three common configurations. The final one is  
uncommon, but it will work and may be useful as a level  
translator; the input stage is run from 5.2V and ground  
while the output stage is run from 3V and ground. In this  
case the common mode input voltage range does not  
include ground, so it may be helpful to tie VCC to 3V.  
Conversely, VCC may also be tied below ground, as long as  
the above rules are not violated.  
Figure 1. Variety of Power Supply Configurations  
Input Voltage Considerations  
The LT1715 is specified for a common mode range of  
–100mV to 3.8V when used with a single 5V supply. A  
more general consideration is that the common mode  
rangeis100mVbelowVEE to1.2VbelowVCC.Thecriterion  
for this common mode limit is that the output still  
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responds correctly to a small differential input signal. If  
oneinputiswithinthecommonmodelimit, theotherinput  
signal can go outside the common mode limits, up to the  
absolute maximum limits, and the output will retain the  
correct polarity.  
equal to the supply voltage, limited only by the absolute  
maximum currents noted. External input protection cir-  
cuitry is only needed if currents would otherwise exceed  
these absolute maximums. The internal catch diodes can  
conduct current up to these rated maximums without  
latchup, even when the supply voltages are at the absolute  
maximum ratings.  
When either input signal falls below the negative common  
mode limit, the internal PN diode formed with the sub-  
strate can turn on, resulting in significant current flow  
through the die. An external Schottky clamp diode  
between the input and the negative rail can speed up  
recovery from negative overdrive by preventing the sub-  
strate diode from turning on.  
The LT1715 input stage has general purpose internal ESD  
protection for the human body model. For use as a line  
receiver, additional external protection may be required.  
As with most integrated circuits, the level of immunity to  
ESD is much greater when residing on a printed circuit  
boardwherethepowersupplydecouplingcapacitancewill  
limit the voltage rise caused by an ESD pulse.  
When both input signals are below the negative common  
mode limit, phase reversal protection circuitry prevents  
false output inversion to at least 400mV common mode.  
However, the offset and hysteresis in this mode will  
increasedramatically,toasmuchas15mVeach.Theinput  
bias currents will also increase.  
Input Bias Current  
Inputbiascurrentismeasuredwithbothinputsheldat1V.  
As with any PNP differential input stage, the LT1715 bias  
current flows out of the device. It will go to zero on the  
higherofthetwoinputsanddoubleonthelowerofthetwo  
inputs. With more than two diode drops of differential  
input voltage, the LT1715’s input protection circuitry  
activates, and current out of the lower input will increase  
an additional 30% and there will be a small bias current  
intothehigherofthetwoinputpins, of4µAorless. Seethe  
Typical Performance curve “Input Current vs Differential  
Input Voltage.”  
When one input signal goes above the common mode  
range without exceeding a diode drop above the input  
supply rail, the input stage will remain biased and the  
comparator will maintain correct output polarity. Above  
this voltage, the input stage current source will saturate  
completely and the ESD protection diode will forward  
conduct. Once the aberrant input falls back into the com-  
monmoderange,thecomparatorwillrespondcorrectlyto  
valid input signals within less than 10ns.  
High Speed Design Considerations  
When both input signals are above the positive common  
modelimit,theinputstagewillgetdebiasedandtheoutput  
polarity will be random. However, the internal hysteresis  
will hold the output to a valid logic level. When at least one  
of the inputs returns to within the common mode limits,  
recovery from this state will take as long as 1µs.  
Applicationofhighspeedcomparatorsisoftenplaguedby  
oscillations. The LT1715 has 4mV of internal hysteresis,  
which will prevent oscillations as long as parasitic output  
to input feedback is kept below 4mV. However, with the  
2V/ns slew rate of the LT1715 outputs, a 4mV step can be  
created at a 100input source with only 0.02pF of output  
to input coupling. The LT1715’s pinout has been arranged  
tominimizeproblemsbyplacingthesensitiveinputsaway  
from the outputs, shielded by the power rails. The input  
and output traces of the circuit board should also be  
separated, and the requisite level of isolation is readily  
achieved if a topside ground plane runs between the  
output and the inputs. For multilayer boards where the  
ground plane is internal, a topside ground or supply trace  
should be run between the inputs and the output.  
The propagation delay does not increase significantly  
when driven with large differential voltages, but with low  
levels of overdrive, an apparent increase may be seen with  
large source resistances due to an RC delay caused by the  
2pF typical input capacitance.  
Input Protection  
The input stage is protected against damage from large  
differential signals, up to and beyond a differential voltage  
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ThegroundpinoftheLT1715candisturbthegroundplane  
potential while toggling due to the extremely fast on and  
offtimesoftheoutputstage. Therefore, usingagroundfor  
input termination or filtering that is separate from the  
LT1715 Pin 6 ground can be highly beneficial. For ex-  
ample, a ground plane tied to Pin 6 and directly adjacent  
to a 1" long input trace can capacitively couple 4mV of  
disturbance into the input. In this scenario, cutting the  
ground plane between the GND pin and the inputs will cut  
the capacitance and the disturbance down substantially.  
maintain signal integrity. The LT1715 can drive DC termi-  
nations of 200or more, but lower characteristic imped-  
ance traces can be used with series termination or AC  
termination topologies.  
Channel Interactions  
The LT1715’s two channels are designed to be entirely  
independent. However, at frequencies approaching and  
exceeding 100MHz, bond wire inductance begins to inter-  
fere with overlapping switching edges on the two chan-  
nels. Figure 3 shows one channel of the comparator  
toggling at 100MHz with the other channel driven low with  
the scope set to display infinite persistence. Jitter is  
almost nonexistent. Figure 4 displays the same channel at  
100MHz with infinite persistence, but the other channel of  
the comparator is toggling as well at frequencies swept  
from 60MHz to 160MHz. Jitter will occur as rising and  
fallingedgesalignforanynonharmonicornonfundamen-  
tal frequency of the high frequency signal.  
Figure 2 shows a typical topside layout of the LT1715 on  
such a multilayer board. Shown is the topside metal etch  
including traces, pin escape vias, and the land pads for an  
MS10 LT1715 and its adjacent X7R 10nF bypass capaci-  
tors in the 0805 case.  
The ground trace from Pin 6 runs under the device up to  
the bypass capacitor, shielding the inputs from the  
outputs. Note the use of a common via for the LT1715 and  
the bypass capacitors, which minimizes interference from  
highfrequencyenergyrunningaroundthegroundplaneor  
power distribution traces.  
5V  
The supply bypass should include an adjacent 10nF  
ceramic capacitor and a 2.2µF tantalum capacitor no  
farther than 5cm away; use more capacitance on +VS if  
driving more than 4mA loads. To prevent oscillations, it is  
helpful to balance the impedance at the inverting and  
noninverting inputs; source impedances should be kept  
low, preferably 1kor less.  
OUT A  
1V/DIV  
0V  
5ns/DIV  
1715 F03  
The outputs of the LT1715 are capable of very high slew  
rates. To prevent overshoot, ringing and other problems  
with transmission line effects, keep the output traces  
shorter than 10cm, or be sure to terminate the lines to  
Figure 3. Clean 100MHz Toggling  
5V  
OUT A  
1V/DIV  
0V  
1715 F02  
5ns/DIV  
1715 F04  
Figure 2. Typical Topside Metal for Multilayer PCB Layouts  
Figure 4. 100MHz Jitter with Both Channels Driven  
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At frequencies well beyond 100MHz, the toggling of one  
channel may be impaired by toggling on the other. This is  
arathercomplexinteractionofsupplybypassingandbond  
inductance, and it cannot be entirely prevented. However,  
good bypassing and board layout techniques will effec-  
tively minimize it.  
V
OH  
V
HYST  
+
(= V  
– V  
)
TRIP  
TRIP  
V
/2  
HYST  
Power Supply Sequencing  
V
OL  
+
V = V – V  
IN  
IN  
IN  
The LT1715 is designed to tolerate any power supply  
sequencing at system turn-on and power down. In any of  
the previously shown power supply configurations, the  
various supplies can activate in any order without exces-  
sive current drain by the LT1715.  
0
+
V
V
TRIP  
V
TRIP  
+
V
+ V  
2
TRIP  
TRIP  
=
OS  
1715 F05  
Figure 5. Hysteresis I/O Characteristics  
As always, the Absolute Maximum Ratings must not be  
exceeded, either on the power supply terminals or the  
input terminals. Power supply sequencing problems can  
occur when input signals are powered from supplies that  
are independent of the LT1715’s supplies. No problems  
should occur if the input signals are powered from the  
same VCC and VEE supplies as the LT1715.  
LT1715 is the significant reduction in these effects, which  
is important whenever an LT1715 is used to detect a  
threshold crossing in one direction only. In such a case,  
the relevant trip point will be all that matters, and a stable  
offset voltage with an unpredictable level of hysteresis, as  
seenincompetingcomparators, isuseless. TheLT1715is  
many times better than prior generation comparators in  
these regards. In fact, the CMRR and PSRR tests are  
performed by checking for changes in either trip point to  
the limits indicated in the specifications table. Because the  
offset voltage is the average of the trip points, the CMRR  
and PSRR of the offset voltage is therefore guaranteed to  
beatleastasgoodasthoselimits. Thismorestringenttest  
also puts a limit on the common mode and power supply  
dependence of the hysteresis voltage.  
Unused Comparators  
Ifacomparatorisunused, itsoutputshouldbeleftfloating  
tominimizeloadcurrent. Theunusedinputscanbetiedoff  
to the rails and power consumption can be further mini-  
mized if the inputs are connected to the power rails to  
induce an output low. Connecting the inverting input to  
VCC and the noninverting input to VEE will likely be the  
easiest method.  
Additionalhysteresismaybeaddedexternally. Therail-to-  
railoutputsoftheLT1715makethismorepredictablethan  
with TTL output comparators due to the LT1715’s small  
variability of VOH (output high voltage).  
Hysteresis  
The LT1715 includes internal hysteresis, which makes it  
easier to use than many other similar speed comparators.  
The input-output transfer characteristic is illustrated in  
Figure 5 showing the definitions of VOS and VHYST based  
upon the two measurable trip points. The hysteresis band  
makes the LT1715 well behaved, even with slowly moving  
inputs.  
To add additional hysteresis, set up positive feedback by  
adding additional external resistor R3 as shown in Fig-  
ure 6. Resistor R3 adds a portion of the output to the  
threshold set by the resistor string. The LT1715 pulls the  
outputs to +VS and ground to within 200mV of the rails  
withlightloads,andtowithin400mVwithheavyloads.For  
the load of most circuits, a good model for the voltage on  
the right side of R3 is 300mV or +VS – 300mV, for a total  
voltageswingof(+VS300mV)(300mV)=+VS600mV.  
The exact amount of hysteresis will vary from part to part  
as indicated in the specifications table. The hysteresis  
level will also vary slightly with changes in supply voltage  
and common mode voltage. A key advantage of the  
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V
REF  
R1mayalsoberequired.Notethatthecurrentsthroughthe  
R1/R2biasstringshouldbemanytimestheinputcurrents  
oftheLT1715.For5%accuracy,thecurrentmustbeatleast  
20 times the input current, more for higher accuracy.  
R3  
R2  
+
1/2 LT1715  
R1  
Interfacing the LT1715 to ECL  
The LT1715’s comparators can be used in high speed  
applications where Emitter-Coupled Logic (ECL) is de-  
ployed. To interface the output of the LT1715 to ECL logic  
inputs, standard TTL/CMOS to ECL level translators such  
as the 10H124, 10H424 and 100124 can be used. These  
components come at a cost of a few nanoseconds addi-  
tional delay as well as supply currents of 50mA or more,  
andareonlyavailableinquads. Afaster, simplerandlower  
power translator can be constructed with resistors as  
shown in Figure 8.  
INPUT  
1715 F06  
Figure 6. Additional External Hysteresis  
Withthisinmind, calculationoftheresistorvaluesneeded  
isatwo-stepprocess.First,calculatethevalueofR3based  
on the additional hysteresis desired, the output voltage  
swing and the impedance of the primary bias string:  
R3 = (R1 R2)(+VS – 0.6V)/(additional hysteresis)  
Additional hysteresis is the desired overall hysteresis less  
the internal 4mV hysteresis.  
Figure 8a shows the standard TTL to Positive ECL (PECL)  
resistiveleveltranslator.Thistranslatorcannotbeusedfor  
theLT1715,orwithCMOSlogic,becauseitdependsonthe  
820resistortolimittheoutputswing(VOH)oftheall-NPN  
TTL gate with its so-called totem-pole output. The LT1715  
is fabricated in a complementary bipolar process and the  
output stage has a PNP driver that pulls the output nearly  
all the way to the supply rail, even when sourcing 10mA.  
The second step is to recalculate R2 to set the same  
averagethresholdasbefore. Theaveragethresholdbefore  
was set at VTH = (VREF)(R1)/(R1 + R2). The new R2 is  
calculated based on the average output voltage (+VS/2)  
and the simplified circuit model in Figure 7. To assure that  
the comparator’s noninverting input is, on average, the  
same VTH as before:  
Figure 8b shows a three resistor level translator for inter-  
facing the LT1715 to ECL running off the same supply rail.  
No pull-down on the output of the LT1715 is needed, but  
pull-down R3 limits the VIH seen by the PECL gate. This is  
needed because ECL inputs have both a minimum and  
maximum VIH specification for proper operation. Resistor  
valuesaregivenforbothECLinterfacetypes;inbothcases  
it is assumed that the LT1715 operates from the same  
supply rail.  
R2= (VREF – VTH)/(VTH/R1 + (VTH – VS/2)/R3)  
For additional hysteresis of 10mV or less, it is not uncom-  
mon for R2to be the same as R2 within 1% resistor  
tolerances.  
This method will work for additional hysteresis of up to a  
few hundred millivolts. Beyond that, the impedance of R3  
is low enough to effect the bias string, and adjustment of  
V
REF  
Figure 8c shows the case of translating to PECL from an  
LT1715poweredbya3Vsupplyrail.Again,resistorvalues  
are given for both ECL interface types. This time four re-  
sistorsareneeded,althoughwith10KH/E,R3isnotneeded.  
In that case, the circuit resembles the standard TTL trans-  
lator of Figure 8a, but the function of the new resistor, R4,  
is much different. R4 loads the LT1715 output when high  
so that the current flowing through R1 doesn’t forward  
biastheLT1715’sinternalESDclampdiode. Althoughthis  
diode can handle 20mA without damage, normal  
R2′  
V
TH  
R3  
+V  
2
S
V
=
AVERAGE  
R1  
+
1/2 LT1715  
1715 F07  
Figure 7. Model for Additional Hysteresis Calculations  
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5V  
5V  
180Ω  
270Ω  
820Ω  
DO NOT USE FOR LT1715  
LEVEL TRANSLATION. SEE TEXT  
LSTTL  
10KH/E  
(a) STANDARD TTL TO PECL TRANSLATOR  
+V  
S
V
CC  
R2  
R1  
+V  
R1  
R2  
R3  
S
1/2 LT1715  
10KH/E 5V OR 5.2V 510180750Ω  
100K/E  
4.5V  
620180510Ω  
R3  
V
EE  
(b) LT1715 OUTPUT TO PECL TRANSLATOR  
V
ECL  
V
3V  
CC  
R2  
R1  
R4  
V
R1  
R2  
R3  
R4  
ECL  
1/2 LT1715  
10KH/E 5V OR 5.2V 300180OMIT 560Ω  
100K/E  
4.5V  
33018015001000Ω  
R3  
V
EE  
(c) 3V LT1715 OUTPUT TO PECL TRANSLATOR  
V
+V  
S
CC  
R4  
ECL FAMILY  
V
+V  
R1  
R2  
R3  
R4  
ECL  
S
R1  
5V  
3V  
5V  
3V  
5602703301200Ω  
270510300330Ω  
6802703001500Ω  
330390270430Ω  
1715 F08  
1/2 LT1715  
10KH/E  
5.2V  
4.5V  
R2  
R3  
100K/E  
V
EE  
V
ECL  
(d) LT1715 OUTPUT TO STANDARD ECL TRANSLATOR  
Figure 8  
operation and performance of the output stage can be  
impaired above 100µA of forward current. R4 prevents  
this with the minimum additional power dissipation.  
Of course, if the VEE of the LT1715 is the same as the ECL  
negative supply, the GND pin can be tied to it as well and  
+VS grounded. Then the output stage has the same power  
rails as the ECL and the circuits of Figure 8b can be used.  
Finally, Figure 8d shows the case of driving standard,  
negative-rail, ECL with the LT1715. Resistor values are  
givenforbothECLinterfacetypesandforbotha5Vand3V  
LT1715 supply rail. Again, a fourth resistor, R4 is needed  
to prevent the low state current from flowing out of the  
LT1715, turning on the internal ESD/substrate diodes.  
Resistor R4 again prevents this with the minimum addi-  
tional power dissipation.  
For all the dividers shown, the output impedance is about  
110. This makes these fast, less than a nanosecond,  
with most layouts. Avoid the temptation to use speedup  
capacitors. Not only can they foul up the operation of the  
ECL gate because of overshoots, they can damage the  
ECL inputs, particularly during power-up of separate  
supply configurations.  
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The level translator designs assume one gate load. Mul-  
tiple gates can have significant IIH loading, and the trans-  
missionlineroutingandterminationissuesalsomakethis  
case difficult.  
The input stage topology maximizes the input dynamic  
range available without requiring the power, complexity  
and die area of two complete input stages such as are  
found in rail-to-rail input comparators. With a single 2.7V  
supply, the LT1715 still has a respectable 1.6V of input  
common mode range. The differential input voltage range  
is rail-to-rail, without the large input currents found in  
competing devices. The input stage also features phase  
reversal protection to prevent false outputs when the  
inputs are driven below the –100mV common mode  
voltage limit.  
ECL, and particularly PECL, is valuable technology for  
high speed system design, but it must be used with care.  
With less than a volt of swing, the noise margins need to  
be evaluated carefully. Note that there is some degrada-  
tion of noise margin due to the ±5% resistor selections  
shown. With 10KH/E, there is no temperature compensa-  
tion of the logic levels, whereas the LT1715 and the  
circuits shown give levels that are stable with tempera-  
ture. This will lower the noise margin over temperature.  
Insomeconfigurationsitispossibletoaddcompensation  
with diode or transistor junctions in series with the  
resistors of these networks.  
Theinternalhysteresisisimplementedbypositive,nonlin-  
ear feedback around a second gain stage. Until this point,  
the signal path has been entirely differential. The signal  
path is then split into two drive signals for the upper and  
lower output transistors. The output transistors are con-  
nected common emitter for rail-to-rail output operation.  
The Schottky clamps limit the output voltages at about  
300mVfromtherail, notquitethe50mVor15mVofLinear  
Technology’s rail-to-rail amplifiers and other products.  
But the output of a comparator is digital, and this output  
stagecandriveTTLorCMOSdirectly.ItcanalsodriveECL,  
as described earlier, or analog loads.  
For more information on ECL design, refer to the ECLiPS  
data book (DL140), the 10KH system design handbook  
(HB205) and PECL design (AN1406), all from Motorola,  
now ON Semiconductor.  
Circuit Description  
The block diagram of the LT1715 is shown in Figure 9. The  
circuit topology consists of a differential input stage, a  
gain stage with hysteresis and a complementary com-  
mon-emitter output stage. All of the internal signal paths  
utilize low voltage swings for high speed at low power.  
The bias conditions and signal swings in the output stage  
are designed to turn their respective output transistors off  
faster than on. This helps minimize the surge of current  
from +VS to ground that occurs at transitions, to minimize  
+V  
S
NONLINEAR STAGE  
+
V
CC  
+
Σ
+IN  
–IN  
+
+
A
A
OUT  
V1  
V2  
+
Σ
+
V
EE  
GND  
1715 F09  
Figure 9. LT1715 Block Diagram  
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thefrequency-dependentincreaseinpowerconsumption.  
The frequency dependence of the supply current is shown  
in the Typical Performance Characteristics.  
will easily leave this undesired operating mode no worse  
for the wear provided there is adequate heat sinking to  
prevent thermal overload. At frequencies well beyond the  
maximumtogglerate,thepartwilltogglewithlimitedoutput  
swing and well controlled power consumption.  
Speed Limits  
The LT1715 comparator is intended for high speed appli-  
cations, where it is important to understand a few limita-  
tions. These limitations can roughly be divided into three  
categories: input speed limits, output speed limits, and  
internal speed limits.  
The internal speed limits manifest themselves as disper-  
sion. All comparators have some degree of dispersion,  
defined as a change in propagation delay versus input  
overdrive. The propagation delay of the LT1715 will vary  
with overdrive, from a typical of 4ns at 20mV overdrive to  
6ns at 5mV overdrive (typical). The LT1715’s primary  
source of dispersion is the hysteresis stage. As a change  
of polarity arrives at the gain stage, the positive feedback  
of the hysteresis stage subtracts from the overdrive avail-  
able. Only when enough time has elapsed for a signal to  
propagate forward through the gain stage, backwards  
through the hysteresis path and forward through the gain  
stage again, will the output stage receive the same level of  
overdrive that it would have received in the absence of  
hysteresis.  
There are no significant input speed limits except the  
shunt capacitance of the input nodes. If the 2pF typical  
input nodes are driven, the LT1715 will respond.  
Theoutputspeedisconstrainedbythreemechanisms,the  
firstofwhichistheslewcurrentsavailablefromtheoutput  
transistors. To maintain low power quiescent operation,  
the LT1715 output transistors are sized to deliver 35mA to  
60mAtypicalslewcurrents.Thisissufficienttodrivesmall  
capacitive loads and logic gate inputs at extremely high  
speeds. But the slew rate will slow dramatically with heavy  
capacitive loads. Because the propagation delay (tPD)  
definition ends at the time the output voltage is halfway  
between the supplies, the fixed slew current makes the  
LT1715fasterat3Vthan5Vwithlargecapacitiveloadsand  
sufficient input overdrive.  
The LT1715 is several hundred picoseconds faster when  
VEE = 5V, relative to single supply operation. This is due  
totheinternalspeedlimit;thegainstageoperatesbetween  
VEE and +VS, and it is faster with higher reverse voltage  
bias due to reduced silicon junction capacitances.  
Inmanyapplications, asshowninthefollowingexamples,  
there is plenty of input overdrive. Even in applications  
providing low levels of overdrive, the LT1715 is fast  
enough that the absolute dispersion of 2ns (= 6 – 4) is  
often small enough to ignore.  
Another manifestation of this output speed limit is skew,  
the difference between tPD+ and tPD. The slew currents of  
the LT1715 vary with the process variations of the PNP  
and NPN transistors, for rising edges and falling edges  
respectively. The typical 0.5ns skew can have either polar-  
ity, rising edge or falling edge faster. Again, the skew will  
increase dramatically with heavy capacitive loads.  
The gain and hysteresis stage of the LT1715 is simple,  
short and high speed to help prevent parasitic oscilla-  
tions while adding minimum dispersion. This internal  
“self-latch” can be usefully exploited in many applica-  
tions because it occurs early in the signal chain, in a low  
power, fully differential stage. It is therefore highly im-  
mune to disturbances from other parts of the circuit,  
such as the output, or on the supply lines. Once a high  
speedsignaltripsthehysteresis, theoutputwillrespond,  
after some propagation delay, without regard to these  
externalinfluencesthatcancausetroubleinnonhysteretic  
comparators.  
Afinallimittooutputspeedistheturn-onandturn-offtime  
of the output devices. Each device has substantial base  
charge that requires one nanosecond or more of active  
chargingordischargingbythebiascurrentoftheDarlington  
driverstage.Whentoggleratesarehighenoughthatinsuf-  
ficient time is allowed for this turn-on or turn-off, glitches  
mayoccurleadingtodropoutorruntpulses. Furthermore,  
power consumption may increase nonlinearly if devices  
are not turned off before the opposing cycle. However,  
oncethetogglefrequencyincreasesordecreases, thepart  
14  
LT1715  
W U U  
APPLICATIO S I FOR ATIO  
U
±VTRIP Test Circuit  
Becausethetrianglewaveisattenuated1000:1andfedto  
the LT1715’s differential input, the sampled voltages are  
therefore 1000 times the input trip voltages. The hyster-  
esisandoffsetarecomputedfromthetrippointsasshown.  
Theinputtrippointstestcircuitusesa1kHztrianglewave  
torepeatedlytripthecomparatorbeingtested.TheLT1715  
output is used to trigger switched capacitor sampling of  
the triangle wave, with a sampler for each direction.  
W
W
SI PLIFIED SCHE ATIC  
V
+V  
S
CC  
150  
–IN  
OUTPUT  
150Ω  
+IN  
GND  
V
EE  
1715 SS  
U
PACKAGE DESCRIPTIO  
Dimensions in inches (millimeters) unless otherwise noted.  
MS10 Package  
10-Lead Plastic MSOP  
(LTC DWG # 05-08-1661)  
0.118 ± 0.004*  
(3.00 ± 0.102)  
0.034  
(0.86)  
REF  
0.043  
(1.10)  
MAX  
10 9  
8
7 6  
0.007  
(0.18)  
0° – 6° TYP  
0.118 ± 0.004**  
(3.00 ± 0.102)  
0.193 ± 0.006  
(4.90 ± 0.15)  
SEATING  
PLANE  
0.007 – 0.011  
(0.17 – 0.27)  
0.021 ± 0.006  
(0.53 ± 0.015)  
0.005 ± 0.002  
(0.13 ± 0.05)  
0.0197  
(0.50)  
BSC  
MSOP (MS10) 1100  
1
2
3
4 5  
* DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH,  
PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE  
** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.  
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE  
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.  
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-  
tation that the interconnection ofits circuits as described herein willnotinfringe on existing patentrights.  
15  
LT1715  
U
TYPICAL APPLICATIO  
High Performance Sine Wave  
to Square Wave Converter  
Similar delay performance is achieved with input frequen-  
ciesashighas50MHz.Thereis,however,someadditional  
encroachment into the central flat zone by both the small  
amplitude and large amplitude variations.  
Propagationdelayofcomparatorsistypicallyspecifiedfor  
a 100mV step with some fraction of that for overdrive. But  
in many signal processing applications, such as in com-  
munications, the goal is to convert a sine wave, such as a  
carrier, to a square wave for use as a timing clock. The  
desired behavior is for the output timing to be dependent  
on the input timing only. No phase shift should occur as a  
function of the input amplitude, which would result in AM  
to FM conversion.  
With small input signals, the hysteresis and dispersion  
make the LT1715 act like a comparator with a 12mV  
hysteresis span. In other words, a 12mVP-P sine wave at  
10MHzwillbarelytoggletheLT1715,with90°ofphaselag  
or 25ns additional delay.  
Above 5VP-P at 10MHz, the LT1715 delay starts to de-  
crease due to internal capacitive feed-forward in the input  
stage. Unlike some comparators, the LT1715 will not  
falsely anticipate a change in input polarity, but the feed-  
forward is enough to make a transition propagate through  
the LT1715 faster once the input polarity does change.  
The circuit of Figure 12a is a simple LT1715-based sine  
wave to square wave converter. The ±5V supplies on the  
input allow very large swing inputs, while the 3V logic  
supply keeps the output swing small to minimize cross  
talk. Figure 12b shows the time delay vs input amplitude  
with a 10MHz sine wave. The LT1715 delay changes just  
0.65ns over the 26dB amplitude range; 2.33° at 10MHz.  
ThedelayisparticularlyflatyieldingexcellentAMrejection  
from 0dBm to 15dBm. If a 2:1 transformer is used to drive  
the input differentially, this exceptionally flat zone spans  
5dBm to 10dBm, a common range for RF signal levels.  
5
4
25°C  
V
V
= 5V  
CC  
EE  
= 5V  
3
2
+V = 3V  
S
10MHz  
5V  
3V  
SINE WAVE  
INPUT  
SQUARE WAVE  
OUTPUT  
+
1
0
632mV  
0
2V  
6.32V  
P-P  
P-P  
P-P  
50Ω  
1/2 LT1715  
–5  
5
10  
15  
20  
25  
INPUT AMPLITUDE (dBm)  
–5V  
1715 F12a  
1715 F12b  
Figure 12a. LT1715-Based Sine Wave to Square Wave Converter  
Figure 12b. Time Delay vs Sine Wave Input Amplitude  
RELATED PARTS  
PART NUMBER  
LT1016  
DESCRIPTION  
COMMENTS  
UltraFast Precision Comparator  
Industry Standard 10ns Comparator  
Single Supply Version of LT1016  
6mA Single Supply Comparator  
UltraFast Rail-to-Rail Input and Output Comparator  
LT1116  
12ns Single Supply Ground-Sensing Comparator  
7ns, UltraFast, Single Supply Comparator  
4.5ns, 3V/5V/±5V Single/Dual Rail-to-Rail Comparators  
LT1394  
LT1711/LT1712  
LT1713/LT1714  
LT1719  
7ns, Low Power, 3V/5V/±5V Single/Dual Rail-to-Rail Comparators  
4.5ns Single Supply 3V/5V Comparator  
Rail-to-Rail Input and Output Comparator  
Single Comparator Similar to the LT1715  
Dual/Quad Comparator Similar to the LT1715  
LT1720/LT1721  
Dual/Quad 4.5ns, Single Supply 3V/5V Comparator  
1715f LT/TP 0401 4K • PRINTED IN USA  
16 LinearTechnology Corporation  
1630 McCarthy Blvd., Milpitas, CA 95035-7417  
LINEAR TECHNOLOGY CORPORATION 2001  
(408)432-1900 FAX:(408)434-0507 www.linear-tech.com  

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