ML13158 [LANSDALE]

Wideband FM IF Subsystem For Dect and Digital Applications; 宽带调频中频子系统,用于DECT和数字应用
ML13158
型号: ML13158
厂家: LANSDALE SEMICONDUCTOR INC.    LANSDALE SEMICONDUCTOR INC.
描述:

Wideband FM IF Subsystem For Dect and Digital Applications
宽带调频中频子系统,用于DECT和数字应用

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ML13158  
Wideband FM IF Subsystem  
For Dect and Digital Applications  
Legacy Device: Motorola MC13158  
The ML13158 is a wideband IF subsystem that is designed for high per-  
formance data and analog applications. The ML13158 has an on–board  
grounded collector VCO transistor that may be used with a fundamental  
or overtone crystal in single channel operation or with a PLL in  
multi–channel operation. The mixer is useful to 500 MHz and may be  
used in a balanced differential or a single ended configuration. The IF  
amplifier is split to accommodate two low cost cascaded filters. RSSI  
output is derived by summing the output of both IF sections. A precision  
data shaper has an Off function to shut the output off to save current. An  
enable control is provided to power down the IC for power management  
in battery operated applications.  
QFP 32 = 8P  
PLASTIC QFP PACKAGE  
CASE 873  
CROSS REFERENCE/ORDERING INFORMATION  
Applications include DECT, wideband wireless data links for personal  
and portable laptop computers and other battery operated radio systems  
which utilize GFSK, FSK or FM modulation.  
PACKAGE  
MOTOROLA  
LANSDALE  
QFP 32  
MC13158FTB  
ML13158-8P  
Note: Lansdale lead free (Pb) product, as it  
becomes available, will be identified by a part  
number prefix change from ML to MLE.  
• Designed for DECT Applications  
• 1.8 to 6.0 Vdc Operating Voltage  
• Low Power Consumption in Active and Standby Mode  
• Greater than 600 kHz Detector Bandwidth  
• Data Slicer with Special Off Function  
• Enable Function for Power Down of Battery Operated Systems  
• RSSI Dynamic Range of 80 dB Minimum  
• Low External Component Count  
• Operating Temperature Range – T = –40 to +85°C  
A
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CIRCUIT DESCRIPTION  
GENERAL  
The output of this buffer has an active pull–up but no pull–down,  
so it can also be used as a peak detector. The negative slew rate is  
determined by external capacitance and resistance to the negative  
supply.  
The ML13158 is a low power single conversion wideband FM receiver  
incorporating a split IF. This device can be used as the backend in digi-  
tal FM systems such as Digital European Cordless Telephone (DECT)  
and wide band data links with data rates up to 2.0 Mbps. It contains a  
mixer, oscillator, Received Signal Strength Indicator (RSSI), IF ampli-  
fier, limiting IF, quadrature detector, power down or enable function,  
and a data slicer with output off function. Further details are covered in  
the Pin Function Description which shows the equivalent internal cir-  
cuit and external circuit requirements.  
IF AMPLIFIER  
The first IF amplifier section is composed of three differential  
stages with the second and third stages contributing to the RSSI.  
This section has internal DC feedback and external input decou-  
pling for improved symmetry and stability. The total gain of the IF  
amplifier block is approximately 40 dB at 10.7 MHz.  
CURRENT REGULATION  
Temperature compensating voltage independent current regulators  
which are controlled by the enable pin (Pin 25) where “low” pow-  
ers up and “high” powers down the entire circuit.  
The fixed internal input impedance is 330 . When using ceramic  
filters requiring source and loss impedances of 330 , no external  
matching is necessary. Overall RSSI linearity is dependent on hav-  
ing total midband attenuation of 10 dB (4.0 dB insertion loss plus  
6.0 dB impedance matching loss) for the filter. The output of the IF  
amplifier is buffered and the impedance is 330 .  
MIXER  
The mixer is a double–balanced four quadrant multiplier and is  
designed to work up to 500 MHz. It can be used in differential or  
in single–ended mode by connecting the other input to the positive  
supply rail. The linear gain of the mixer is approximately 22 dB at  
100 mVrms LO drive level. The mixer gain and noise figure have  
been emphasized at the expense of intermodulation performance.  
RSSI measurements are added in the mixer to extend the range to  
higher signal levels. The single–ended parallel equivalent input  
impedance of the mixer is Rp ~ 1.0 kand Cp ~ 2.0 pF. The  
buffered output of the mixer is internally loaded resulting in an out-  
put impedance of 330 .  
LIMITER  
The limiter section is similar to the IF amplifier section except that  
five differential stages are used. The fixed internal input impedance  
is 330 . The total gain of the limiting amplifier section is approxi-  
mately 70 dB. This IF limiting amplifier section internally drives  
the quadrature detector section and it is also brought out on Pin 12.  
QUADRATURE DETECTOR  
The quadrature detector is a doubly balanced four quadrant multi-  
plier with an internal 5.0 pF quadrature capacitor between Pins 12  
and 13. An external capacitor may be added between these pins to  
increase the IF signal to the external parallel RLC resonant circuit  
that provides the 90 degree phase shift and drives the quadrature  
detector. A single pin (Pin 13) provides for the external LC parallel  
resonant network and the internal connection to the quadrature  
detector.  
LOCAL OSCILLATOR  
The on–chip transistor operates with crystal and LC resonant ele-  
ments up to 220 MHz. Series resonant, overtone crystals are used  
to achieve excellent local oscillator stability. Third overtone crys-  
tals are used through about 65 to 70 MHz. Operation from 70 MHz  
up to 180 MHz is feasible using the on–chip transistor with a 5th  
or 7th overtone crystal. To enhance operation using an overtone  
crystal, the internal transistor bias is increased by adding an exter-  
Internal low pass filter capacitors have been selected to control the  
bandwidth of the detector. The recovered signal is brought out by  
the inverting amplifier buffer. An external feedback resistor from  
the output (Pin 17) to the output amplitude; it is combined with  
another external resistor from the input to the negative supply (Pin  
15) controls the output amplitude; it is combined with another  
external resistor from the input to the negative supply (Pin 16) to  
set the output DC level. For a resistor ratio of 1, the DC level at the  
nal resistor from Pin 29 to V , however, with an external resistor,  
EE  
the oscillator stays on during power down. Typically, –10 dBm of  
local oscillator drive is needed to adequately drive the mixer. With  
an external oscillator source, the IC can be operated up to 500  
MHz.  
RSSI  
The Received Signal Strength Indicator (RSSI) output is a current  
proportional to the log of the received signal amplitude. The RSSI  
current output is derived by summing the currents from the mixer,  
IF and limiting amplifier stages. An increase in RSSI dynamic  
range, particularly at higher input signal levels is achieved. The  
RSSI circuit is designed to provide typically 85 dB of dynamic  
range with temperature compensation.  
detector output is 2.0 V  
across the first resistor (from Pin 17 to 15) can be used to reduce  
the bandwidth.  
(see Figure 12). A small capacitor C  
17  
BE  
DATA SLICER  
The data slicer is a comparator that is designed to square up the  
data signal. Across the data slicer inputs (Pins 18 and 20) are back  
to back diodes.  
Linearity of the RSSI is optimized by using external ceramic band-  
pass filters which have an insertion loss of 4.0 dB and 330 Ω  
source and load impedance. For higher data rates used in DECT  
and related applications, LC bandpass filtering is necessary to  
acquire the desired bandpass response; however, the RSSI linearity  
will require the same insertion loss.  
The recovered data signal from the quadrature detector can be DC  
coupled to the data slicer DS IN1 (Pin 18). In the application cir-  
cuit shown in Figure 1 it will be centered at 2.0 V  
and allowed  
. A capacitor is placed from DS IN2 (Pin 20) to  
BE  
to swing  
EE  
V
BE  
V
. The size of this capacitor and the nature of the data slicer  
shapes up the recovered signal. The time constant is short for large  
peak to peak voltage swings or when there is a change in DC level  
at the detector output. For small signal or for continuous bits of the  
same polarity which drift close to the threshold voltage, the time  
RSSI BUFFER  
The RSSI output current creates a voltage across an external resis-  
tor. A unity voltage–gain amplifier is used to buffer this voltage.  
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constant is longer.  
shut off by shutting down the base drive to the output transistor.  
When a channel is being monitored to make an RSSI measurement,  
A unique feature of the data slicer is that inverting switching stages but not to collect data, the data output may be shut off to save cur-  
in the comparator are supplied through the emitter pin of the output rent.  
transistor (Pin 22 – DS Gnd) to V rather than internally to V  
.
EE EE  
This is provided in order to reduce switching feedback to the front  
end. A control pin is provided to shut the data slicer output off (DS  
“off” – Pin 19). With DS “offpin at V  
the data slicer output is  
CC  
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Legacy Applications Information  
APPLICATIONS INFORMATION  
EVALUATION PC BOARD  
COMPONENT SELECTION  
The evaluation PCB is very versatile and is intended to be used  
across the entire useful frequency range of this device. The center  
section of the board provides an area for attaching all SMT compo-  
The evaluation PC board is designed to accommodate specific  
components, while also being versatile enough to use components  
from various manufacturers and coil types. Figures 13 and 14 show  
nents to the circuit side and radial leaded components to the compo- the placement for the components specified in the application cir-  
nent ground side (see Figures 29 and 30). Additionally, the peripher- cuit (Figure 12). The application circuit schematic specifies particu-  
al area surrounding the RF core provides pads to add supporting and lar components that were used to achieve the results shown in the  
interface circuitry as a particular application requires. This evalua-  
tion board will be discussed and referenced in this section.  
typical curves and tables but alternate components should give sim-  
ilar results.  
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INPUT MATCHING/COMPONENTS  
kin parallel with 2.0 pF; thus, no or little input matching is  
required between the SAW filter and the mixer.  
It is desirable to use a SAW filter before the mixer to provide addi-  
tional selectivity and adjacent channel rejection. In a wideband sys-  
tem the primary sensitivity of the receiver backend may be  
The Siemens SAW filter has an insertion loss of typically 10 dB  
achieved before the last mixer. Bandpass filtering in the limiting IF and a 3.0 dB bandwidth of 1.0 MHz. The relatively high insertion  
is costly and difficult to achieve for bandwidths greater than 280  
kHz.  
loss significantly contributes to the system noise and a filter having  
lower insertion loss would be desirable. In existing low loss SAW  
filters, the required load impedance is 50 ; thus, interface match-  
ing between the filter and the mixer will be required. Figure 15 is a  
The SAW filter should be selected to easily interface with the  
mixer differential input impedance of approximately 2.0 kin par- table of the single–ended mixer input impedance. A careful noise  
allel with 1.0 pF. The PC board is dedicated to the Siemens SAW  
analysis is necessary to determine the secondary contribution to  
filter (part number Y6970M); the part is designed for DECT at 112 system noise.  
MHz 1st IF frequency. It is designed for a load impedance of 2.0  
SYSTEM NOISE CONSIDERATIONS  
The system block diagram in Figure 16 shows the cascaded noise  
F3 = the Noise factor of the Mixer  
Note: the proceeding terms are defined as linear relationships and  
stages contributing to the system noise; it represents the application are related to the log form for gain and noise figure by the follow-  
circuit in Figure 12 and a low noise preamp using a MRF941 trans- ing:  
–1  
F = log [(NF in dB)/10] and similarly  
lator (see Figure 17). The preamp is designed for a conjugately  
matched input and output at 2.0 Vdc. V and 3.0 mAdc I . S-  
CE  
c
–1  
parameters at 2.0 V, 3.0 mA and 100 MHz are:  
G = log [(NF in dB)/10]  
S11 = 0.86, –20  
S21 = 9.0, 164  
S12 = 0.02, 79  
S22 = 0.96, –12  
The noise figure and gain measured in dB are shown in the system  
block diagram. The mixer noise figure is typically 14 dB and the  
SAW filter adds typically 10 dB insertion loss. Addition of a low  
noise preamp having a 18 dB gain and 2.7 dB noise figure not only  
improves th system noise figure but it increases the reverse isola-  
tion from the local oscillator to the antenna input at the receiver.  
Calculating in terms of gain and noise factor yields the following:  
F1 = 1.86; G1 = 63.1  
The bias network and V at 2.0 V and I at 3.0 mA for V = 3.0  
CE  
c
CC  
to 3.5 Vdc. The preamp operates with 18 dB gain and 2.7 dB noise  
figure.  
In the cascaded noise analysis the system noise equation is:  
Fsystem = F1 + [(F2–1)/G1] + [(F3–1)]/[(G1)(G2)]  
where:  
F2 = 10; G2 = 0.1  
F1 = the Noise Factor of the Preamp  
G1= the Gain of the Preamp  
F2 = the Noise factor of the SAW filter  
G2 = the Gain of the SAW filter  
F3 = 25.12  
Thus, substituting in the equation for system noise factor:  
Fsystem = 5.82; NFsystem = 7.7 dB  
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Legacy Applications Information  
LOCAL OSCILLATORS  
VHF APPLICATIONS  
The on–chip grounded collector transistor may be used for HF and  
VHF local oscillator with higher order overtone crystals. The local  
traces and tap capacitors. Parasitic oscillations often occur in the  
200 to 800 MHz range. A small resistor is placed in series with the  
base (Pin 28) to cancel the negative resistance associated with this  
oscillator in the application circuit (Figure 12) shows a 5th overtone undesired mode of oscillation. Since the base input impedance is so  
oscillator at 122.7 MHz. This circuit uses a Butler overtone oscilla- large a small resistor in the range of 27 to 68 has very little effect  
tor configuration. The amplifier is an emitter follower. The crystal  
is driven from the emitter and is coupled to the high impedance  
base through a capacitive tap network. Operation at the desired  
overtone frequency is ensured by the parallel resonant circuit  
formed by the variable inductor and the tap capacitor and parasitic  
capacitances of the on–chip transistor and PC board. The variable  
inductor specified in the schematic could be replaced with a high  
tolerance, high Q ceramic or air wound surface mount component  
if the other components have tight enough tolerances. A variable  
on the desired Butler mode of oscillation.  
The crystal parallel capacitance, C , provides a feedback path that  
o
is low enough in reactance at frequencies of 5th overtones or higher  
to cause trouble. C has little effect near resonance because of the  
o
low impedance of the crystal motional arm (R –L –C ). As the  
m
m
m
tunable inductor which forms the resonant tank with the tap capaci-  
tors is tuned “offthe crystal resonant frequency it may be difficult  
to tell if the oscillation is under crystal control. Frequency jumps  
inductor provides an adjustment for gain and frequency of the reso- may occur as the inductor is tuned. In order to eliminate this behav-  
nant tank ensuring lock up and start– up of the crystal oscillator. ior an inductor, L , is placed in parallel with the crystal. L is cho-  
The overtone crystal is chosen with ESR of typically 80 and 120 sen to be resonant with he crystal parallel capacitance, C , at the  
o
o
o
maximum; if the resistive loss in the crystal is too high the per-  
formance of oscillator may be impacted by lower gain margins.  
desired operation frequency. The inductor provides a feedback path  
at frequencies well below resonance; however, the parallel tank net-  
work of the tap capacitors and tunable inductor prevent oscillation  
A series LC network to ground (which is V ) is comprised of the at these frequencies.  
CC  
inductance of the base lead of the on–chip transistor and PC board  
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Legacy Applications Information  
IF FILTERING/MATCHING  
Substitue for Requivalent and solve for Rext  
In wideband data systems the IF bandpass needed is greater than  
can be found in low cost ceramic filters operating at 10.7 MHz. It  
is necessary to bandpass limit with LC networks or series–parallel  
ceramic filter networks. Murata offers a series–parallel resonator  
pair (part number KMFC545) with a 3.0 dB band width of 325  
kHz and a maximum insertion loss of 5.0 dB. The application PC  
board is laid out to accommodate this filter pair (a filter pair is used  
at both locations of the split IF). However, even using a series par-  
allel ceramic filter network yields only a maximum bandpass of  
650 kHz. In some applications a wider band IF bandpass is neces-  
sary.  
330(Rext) = 110 (Rext) + (330)(110)  
Rext = (330)(110)/220  
Rext - 165 Ω  
The IF is 10.7 Mhz although any IF between 10 to 20 MHz could  
be used. The value of the coil is lowered from that used in the  
quadrature circuit because the unloaded Q must be maintained in a  
surface mount component. A standard value component having an  
unloaded Q = 100 at 10.7 MHz is 330 nH; therefore the capacitor  
is 669 pF. Standard values have been chosen for these components;  
Rext = 150 Q  
C = 680 pF  
L = 330 nH  
A simple LC network yields a bandpass wider than the SAW filter  
but it does reduce an appreciable amount of wideband IF noise. In  
the application circuit an LC network is specified using surface  
mount components. The parallel LC components are placed from  
Computation of the loaded Q of the is LCR network is  
Q = Requivalent/X  
L
where XL = 2πfl and Requivalent is 103 Ω  
Thus, Q = 4.65  
the outputs of the mixer and IF amplifier to the V  
trace; internal  
The total system loss is  
CC  
330loads are connected from the mixer and IF amplifier outputs  
DEC2 (Pin 5 and 10 respectively). This loads the outputs with the  
optimal load impedance but creates a low insertion loss filter. An  
external shunt resistor may be used to widen the bandpass and to  
acquire the 10 dB composite loss necessary to linearize the RSSI  
output. The equivalent circuit is shown in Figure 18.  
20 log (103/433) = –12.5 dB  
QUADRATURE DETECTOR  
The quadrature detector is coupled to the IF with an internal 5.0 pF  
capacitor between Pins 12 and 13. For wideband data applications,  
the drive to the detector can be increased with an additional exter-  
nal capacitor between these pins; thus, the recovered signal level  
output is increased for a given bandwidth.  
The wideband performance of the detector is controlled by the  
loaded Q of the LC tank circuit. The following equation defines the  
components which set the detector circuits bandwidth:  
Q = R /X  
[1]  
T L  
where RT is the equivalent shunt resistance across the LC Tank  
XL is the reactance of the quadrature inductor at the IF fre-  
quency (X = 2πfl).  
L
The inductor and capacitator are chosen to form a resonant LC tank  
with the PCB and parasitic device capacitance at the desired IF  
center frequency as predicted by  
1/2 –1  
fc = [2π (LC )  
]
[2]  
p
where L is the parallel tank inductor Cp is the equivalent parallel  
capacitance of the parallel resonant tank circuit.  
The following is a design example for a wideband detector at 10.7  
MHz and a loaded Q of 18. The loaded Q of the quadrature detec-  
tor is chosen somewhat less than the Q of the IF bandpass. For an  
IF frequency of 10.7 MHz and an IF bandpass of 600 kHz, the IF  
bandpass Q is approximately 6.4.  
The following equations satisfy the 12 dB loss  
(1:4 resistive ratio):  
(Rext)(330)/(Rext + 330) = Requivalent  
Requivalent/Requivalent + 330) = 1/4  
Solve for Requivalent:  
4(Requivalent) = Requivalent + 330  
3(Requivalent) = 330  
Requivalent = 110  
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EXAMPLE:  
Let the external Cext = 139 pF. (The miminum value here should  
be much greater than the internal device and PCB parasitic capaci-  
tance, Cint = 3.0 pF.). Thus, Cp = Cint + Cext = 142 pF.  
Rewrite equation (2) and solve for L  
2
2
L = (0.159) /(Cpfc )  
L = 1.56 µH; Thus, a standard value is chosen:  
L = 1.56 µH (tunable shielded inductor)  
The value of the total damping resistor to obtain the required  
loaded Q of 18 can be calculated by rearranging equation (1):  
R = Q(2πfl)  
T
R = 18(2π)(10.7)(1.5) = 1815Ω  
T
The internal resistance, Rint at the quadrature tank Pin 13 is  
approximately 13 kand is considered in determining the external  
resistance, Rext which is calculated from  
DATA SLICER CIRCUIT  
at the input of the data slicer is chosen to maintian a time con-  
Rext = ((R )(Rint))/(Rint – R )  
C
20  
T
T
Rext = 2110; Thus choose the standard value  
Rext = 2.2 kΩ  
stant long enought to hold the charge on the capacitor for the  
longest strings of bits at the same polarity. For a data rate of 576  
kHz a bit stream of 15 bits at the same plarity would equate to an  
apparent data rate of approximately 77 kbps or 38 kHz. The time  
constant would be approximately 26 µs. The following expression  
equates the time constant t, to the external components;  
It is important to set the DC level of the detector output at Pin 17 to  
center the peak to peak swing of the recovered signal. In the equiv-  
alent internal circuit shown in the Pin Function Description, the ref-  
erence voltage at the positive terminal of the inverting, op amp  
buffer amplifier is set at 1.0 V . The detector DC level, V is  
t = 2π (R )(C )  
BE  
17  
18 20  
determined by the following equation:  
Solve for C :  
20  
V
17  
= [((R /R ) + 1 )/(R /R )] V  
C
20  
= t/2π (R )  
15 17 15 17 BE  
18  
where the effective resistance R is a complex function of the  
Thus for a 1:1 ratio of R /R , V = 2.0 V = 1.4 Vdc.  
Similarly for a 2:1, V = 1.5 V = 1.05 Vdc; and for 3:1, V  
17 BE 17  
1.33 V = 0.93 Vdc.  
BE  
18  
15 17 17 BE  
demodulator feedback resistance and data slicer input circuit. In the  
data input network the back to back diodes form a charge and dis-  
charge path for the capacitor at Pin 20; however, the diodes create a  
non–linear response. This resistance is loaded by the ß, beta of the  
detector output transistor; beta = 100 is a typical value (see Figure  
21). Thus, the apparent value of the resitance at Pin 18 (DS IN1) is  
approximately equal to:  
=
Figure 19 shows the detector “S–Curves”, in which the resistor  
ratio is varied while maintaining a constant gain (R is held at 62  
17  
k). R is 62 kfor a 1:1 ratio; while R = 120 kand 180 kΩ  
15  
15  
to produce the 2:1 and 3:1 ratio. The IF signal into the detector is  
swept 500 KHz about the 10.7 MHz, IF center frequency. The  
resulting curve show how the resistor ratio and the supply voltage  
effects the symmetry of the “S–curve” (Figure 21 Test Setup). For  
R
18  
~ R /100  
17  
where R is 82 k, the feedback resistor from Pin 17 to 15.  
17  
Therefore, substituting for R and solving for C :  
18  
20  
C
20  
= 15.9 (t)/R = 5.04 nF  
the 3:1 and 2:1 ratio, symmetry is maintained with V from 2.0 to  
17  
S
The closest standard value is 4.7 nF.  
5.0 Vdc; however, for the 1:1 ratio, symmetry is lost at 2.0 Vdc.  
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Legacy Applications Information  
RSSI  
In Figure 22, the RSSI versus RF Input Level shows the linear  
response of RSSI over a 65 dB range but it has extended capability  
over 80 dB from –80 dBm to +10 dBm. The RSSI is measured in  
the application circuit (Figure 12) in which a SAW filter is used  
before the mixer; thus, the overall sensitivity is traded off for the  
sake of selectivity. The curves are shown for three filters having  
different bandwidths:  
1) LCR Filter with 2.3 MHz 3.0 dBm BW (Circuit and  
Component Placement is shown in Figure 12)  
2) Series–Parallel Ceramic Filter with 650 kHz 3.0 dB BW  
(Murata Part # KMFC - 545)  
3) Ceramic Filter with 280 kHz 3.0 dB BW.  
SINAD PERFORMANCE  
Figure 24 shows a test setup for a narrowband demodulator output  
response in which a C–message filter and an active de–emphasis  
filter is used following the demodulator. The input is matched using  
a 1:4 impedance transformer. The SINAD performance is shown in  
Figure 25 with no preamp and in Figure 26 with a preamp  
(Preamp–Figure 16). The 12 dB SINAD sensitivity is –101 dBm  
with no preamp and –113 dBm with the preamp.  
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Legacy Applications Information  
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Issue B  
ML13158  
LANSDALE Semiconductor, Inc.  
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Issue B  
ML13158  
LANSDALE Semiconductor, Inc.  
Lansdale Semiconductor reserves the right to make changes without further notice to any products herein to improve reliabili-  
ty, function or design. Lansdale does not assume any liability arising out of the application or use of any product or circuit  
described herein; neither does it convey any license under its patent rights nor the rights of others. “Typical” parameters which  
may be provided in Lansdale data sheets and/or specifications can vary in different applications, and actual performance may  
vary over time. All operating parameters, including “Typicals” must be validated for each customer application by the customer’s  
technical experts. Lansdale Semiconductor is a registered trademark of Lansdale Semiconductor, Inc.  
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Issue B  

相关型号:

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