LMX2240MX [NSC]
IC SPECIALTY TELECOM CIRCUIT, PDSO16, PLASTIC, SOP-16, Telecom IC:Other;
| 型号： | LMX2240MX |
| 厂家： | 
National Semiconductor |
| 描述： | IC SPECIALTY TELECOM CIRCUIT, PDSO16, PLASTIC, SOP-16, Telecom IC:Other 电信 信息通信管理 光电二极管 电信集成电路 |
| 文件： | 总12页 (文件大小：206K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
April 1995
LMX2240
Intermediate Frequency Receiver
General Description
Features
Y
Typical operation at 110 MHz
b
RF sensitivity to 75 dBm; RSSI sensitivity to
The LMX2240 is a monolithic, integrated intermediate fre-
quency receiver suitable for use in Digital European Cord-
less Telecommunications (DECT) systems as well as other
mobile telephony and wireless communications applica-
tions. It is fabricated using National’s ABiCTM IV BiCMOS
Y
b
High gain (70 dB) limiting amplifier
82 dBm
Y
Y
Average current consumption: 480 mA for DECT
handset (burst mode)
e
process (f
15 GHz).
T
Y
Y
Y
The LMX2240 consists of a high gain limiting amplifier, a
frequency discriminator, and a received signal strength indi-
cator (RSSI). The high gain limiting amplifier and discrimina-
tor operate in the 40 MHz to 150 MHz frequency range, and
the limiter has approximately 70 dB of gain. The use of the
limiter and the discriminator provides a low cost, high per-
formance demodulator for communications systems. The
RSSI output can be used for channel quality monitoring.
a
3V operation
Power down mode for increased current savings
Part of a complete receiver solution with the LMX2216
LNA/Mixer, the LMX2315/20 Phase-locked Loop, and
the LMX2411 Baseband Processor
1
Y
TM
Compliant to ARi
specification
Applications
The LMX2240 is intended to support single conversion re-
ceivers. This device saves power, size, and cost by eliminat-
ing the second local oscillator (LO), second converter (mix-
er), and additional filters. The LMX2240 is recommended for
systems with channel bandwidths of 300 kHz to 2.5 MHz.
Y
Digital European Cordless Telecommunications (DECT)
Portable wireless communications (PCS/PCN, cordless)
Wireless local area networks (WLANs)
Y
Y
Y
Y
Digital cellular telephone systems
Other wireless communications systems
The LMX2240 is available in a 16-pin JEDEC surface mount
plastic package.
Functional Block Diagram
TL/W/11755–1
1TM
ABiCTM and ARi
are trademarks of National Semiconductor Corporation.
C
1995 National Semiconductor Corporation
TL/W/11755
RRD-B30M115/Printed in U. S. A.
Connection Diagram
Small Outline Package
TL/W/11755–2
Top View
Order Number LMX2240M
See NS Package Number M16A
Pin Description
Pin No.
Pin Name
PD
I/O
I
Description
1
2
Power Down; a HIGH signal switches the part to power down mode.
Voltage output of the received signal strength indicator (RSSI).
No connection
RSSI Out
NC
O
3
4
GND
Ground
5
GND
Ground
6
MID
O
O
Mid-range output of the discriminator; can be used for comparator threshold.
Demodulated output of the discriminator.
Source voltage for the mixer (discriminator).
Source voltage for the limiter.
7
Demod Out
8
V
(Mixer)
(Lim.)
CC
9
V
CC
10
Quad In
I
Quadrature input. A DC path from source through an inductor must be present at
this pin, but, there must be no series resistance (a parallel resistor to the inductor
is acceptable).
11
12
13
14
Lim. Out
GND
O
Limiter output to the quadrature tank.
Ground
Ground
GND
Comp.
Compensation pin for the limiter. See Applications Information for capacitor
value.
15
16
Comp.
IF In
Compensation pin for the limiter. See Applications Information for capacitor
value.
I
IF input to the limiter.
2
Absolute Maximum Ratings
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales
Office/Distributors for availability and specifications.
Recommended Operating
Conditions
Min
Max
Units
Supply Voltage (V
3V
)
CC
Power Supply Voltage (V
)
CC
6.5V
2.85
b
3.15
a
V
b
a
65 C to 150 C
§
Storage Temperature Range (T )
S
§
Operating Temperature (T )
A
10
70
C
§
Lead Temperature (T )
L
(Soldering, 10 seconds)
a
260 C
§
Electrical Characteristics
The following specifications apply for supply voltage V
specified
e a
e
e
g
3V 5%, f
120 MHz, and T
25 C unless otherwise
§
CC
IN
A
Value
Typ
Symbol
Parameter
Conditions
Min
Max
Units
I
I
Supply Current
8
10
mA
mA
DD
PD
Power Down Current
115
150
10
200
f
Maximum IF Input Frequency
Minimum IF Input Frequency
120
MHz
MHz
max
min
f
IF LIMITER
NF
IF Limiter Noise Figure
Limiter Gain
11.5
70
12.5
225
dB
dB
dBm
X
e
1000X
A
V
Z
L
e
b
75
sens
Limiter/Disc. Sensitivity
IF Limiter Input Impedance
IF Limiter Output Impedance
Maximum Input Voltage Level
Output Swing
BER
0.001
IF
IF
150
350
1.0
in
250
500
500
X
out
max
out
V
V
mV
PP
V
PP
b
70
Lim
Input Limiting Point
dBm
DISCRIMINATOR
V
out
Discriminator Output Peak-to-Peak Voltage
(Note 1)
See Test Circuit
1.2
V
PP
V
Disc. Output DC Voltage (Pin 7)
Mid-Range Output (Pin 6)
Disc. Input Impedance
1.4
1.4
1.7
1.7
V
V
OS
MID
DISC
DISC
1000
150
X
X
in
Disc. Output Impedance
out
RSSI
RSSI
RSSI
RSSI Dynamic Range
RSSI Output Voltage
70
0.5
1.5
16
3
dB
V
e b
Pin
Pin
Pin
80 dBm
0 dBm
e b
0.35
1.15
0.8
1.8
out
e
V
b
RSSI Slope
70 dBm to 20 dBm
11
mV/dB
dB
RSSI Linearity
Note 1: The discriminator output peak-to-peak voltage is measured by operating the discriminator mixer with two separate inputs (i.e., as a mixer). A beat frequency
of 1 kHz is generated, and this tone’s output swing is guaranteed to be at least 1.0 V . When the mixer is configured as a discriminator with the limiter and a tank
PP
) 200 mV demodulated output, assuming at least 36 phase shift across the band of
e
circuit, the guaranteed 1.0 V output translates to (1.0V *(36/180)
PP
interest from the tank circuit.
§
PP
3
Typical Application Block Diagram
TL/W/11755–3
Functional Description
OVERVIEW
THE RECEIVED SIGNAL STRENGTH INDICATOR (RSSI)
The LMX2240 IF demodulator is a low power IF processor
that includes a frequency discriminator, an IF hard limiting
amplifier, and a received signal strength indicator (RSSI).
The LMX2240 is capable of differentially demodulating an
FM or AM signal with as high an IF as 150 MHz, avoiding a
costly second down-conversion. The RSSI output can be
used for time gated channel measurements required in
TDMA and other systems. Other features include high re-
ceiver sensitivity and a power down mode to allow for stand-
by operation.
The RSSI circuit has a range of 70 dB. Its output voltage is
proportional to the logarithm of the input signal level. The
b
RSSI circuit has a sensitivity of 82 dBm. The output volt-
age of the circuit ranges from 0.5V to 1.5V typically.
THE FREQUENCY DISCRIMINATOR
The frequency discriminator is a Gilbert cell mixer that re-
quires an external tank circuit to create a 90 phase shift at
§
the desired frequency. The output of this circuit is centered
at 1.5V by an internal level shifting circuit, and a mid-range
voltage (at 1.5V) is also provided. The sensitivity of the dis-
criminator to phase inaccuracies is 5.5 mV/degree (see Ap-
plications Information). This means that for a phase imbal-
THE LIMITING AMPLIFIER
The limiting amplifier has a typical gain of 70 dB and a sen-
b
sitivity of about 75 dBm. This allows it to be used in the
DECT system with 20 dB net RF gain in front of it to achieve
ance of 10 , the received eye diagram will be shifted by
§
about 55 mV off of the 1.5V mid-range voltage. For the typi-
cal case, this amounts to about 10% of the output eye dia-
b
a sensitivity of 95 dBm. The limiter is a five stage amplifier
with internal compensation at each stage to ensure stability.
Two external compensation capacitors are also required to
further enhance stability. The input to the limiter is a relative-
ly low impedance to allow easy matching to typical IF sur-
face acoustic wave (SAW) filters. The output of the limiter is
connected off chip to an external quadrature tank circuit as
well as connected internally to the discriminator (mixer). The
output impedance of the limiter is 250X (typical).
gram (for 400 mV output).
PP
4
Typical Performance Characteristics
Limiter Gain vs Frequency with
Temperature as a Parameter
TL/W/11755–4
Limiter Gain vs Frequency with
Supply Voltage as a Parameter
TL/W/11755–5
5
Typical Performance Characteristics (Continued)
Discriminator Output Peak-to-Peak Voltage
vs Supply with Temperature as a Parameter
Current Consumption vs Supply Voltage
with Temperature as a Parameter
TL/W/11755–6
TL/W/11755–7
Mid-Range (Reference) Voltage vs Supply
with Temperature as a Parameter
Power Down Current vs Temperature
TL/W/11755–8
TL/W/11755–9
Limiter Output Power vs Frequency
with Voltage as a Paramerer
Limiter Output Power vs Frequency
with Temperature as a Paramerer
TL/W/11755–10
TL/W/11755–11
6
Typical Performance Characteristics (Continued)
RSSI Output vs Input Power
with V as a Parameter
CC
TL/W/11755–12
RSSI Output vs Input Power with
Temperature as a Parameter
TL/W/11755–13
7
Automatic Test Circuit
TL/W/11755–14
e
e
e
e
e
e
e
e
e
e
e
g
1000 pF 10% NPO Ceramic
g
1000 pF 10% NPO Ceramic
C1
C3
R2
L1
C2
R1
R3
C4
C5
g
1000 pF 10% NPO Ceramic
g
25X 5% (/4W Thin Film Carbon
g
g
1 kX 5% (/4W Thin Film Carbon
1 kX 5% (/4W Thin Film Carbon
g
g
1000 pF 10% NPO Ceramic
10 mH 5% Air Coil
g
g
1000 pF 10% NPO Ceramic
R4
R5
20X 5% (/4W Thin Film Carbon
g
3.9 kX 5% (/4W Thin Film Carbon
8
Typical Application Example
TL/W/11755–15
e
e
e
g
e
e
1 pF 10% NPO Ceramic
e
g
100 pF 10% NPO Ceramic
C1
C4
C2
C3
C5
C6
e
e
0.01 mF 10% NPO Ceramic
g
C7
C9
e
e
e
g
82 pF 10% X7R Ceramic
g
C8
R2
R1
4 kX 5% (/4W Thin Film Carbon
e
Ý
Toko 638AH-0294
g
880X 5% (/4W Thin Film Carbon
Tank
All supporting components 0603 surface mount except tank.
9
Applications Information
THE INTERMEDIATE FREQUENCY LIMITER
With a circuit that gives an output peak-to-peak voltage of
1.0 V (min) with ideal quadrature, the slope is seen to be
PP
The IF limiter has a large amount of gain at high enough
frequency to cause concern about oscillation. To ensure
that the limiter does not oscillate, a few precautions should
be taken. The compensation capacitors that are used
should be chosen to roll off any unwanted frequencies be-
low the band of interest. The capacitor should be a high Q,
RF type ceramic chip capacitor. For DECT, the capacitor
value should be 100 pF, and the capacitors should be sol-
dered as close to the LMX2240 as possible. This will create
a pass band from 40 MHz to 150 MHz. The AC coupling
capacitor at the input to the limiter (from the SAW filter)
should be the same value as the compensation capacitors.
5.5 mV/degree. With a practical quadrature tank circuit at
110.6 MHz, the phase shift over a 1 MHz bandwidth is about
45 –50 , which translates to an output peak-to-peak voltage
§
§
of about 250 mV
.
PP
Assume the FM modulated signal is denoted as
e
a
s(t)
cos (0ct
m(t)) ,
t
(4)
e
where m(t)
m
b(t) dt ,
b%
and b(t) is the modulating baseband signal. The con-
#
e
stant m is defined as m
be delayed by some u so that
2DfTb. The signal s(t) must
THE DISCRIMINATOR
e
a
s(t u)
e
a
a
a
There are two types of discriminator that can be used to
demodulate FM signals. The first is a delay line discrimina-
tor, which uses a delay in one path of the received signal to
introduce a phase difference between it and the received
signal. The operation of the delay line discriminator is de-
rived in the inset box. The other type of discriminator relies
on a quadrature tank to directly introduce a phase shift in
the received signal. This is the type of implementation that
is commonly used in mobile communications because of its
relative ease of construction and low cost.
l(t)
cos (0c(t u)
m(t u)) .
(5)
If the delay u is such that
q
e
a
e
0ct
2nq
,
n
0, 1, 2, 3, . . . ,
(6)
(7)
2
a
e
a
a
m(t u)),
then s(t u)
sin(0ct
and multiplying (4) and (7) yields
e
a
a a
m(t u))
s(t) l(t)
cos (0ct
m(t)) sin (0ct
1
e
a
a a
m(t u))
sin (20ct
m(t)
(8)
2
The discriminator operates best when the inputs to it are
hard-limited (i.e., square edges). If the input signal is small
enough such that the IF amplifier cannot limit it, the output
voltage swing of the limiter will suffer. Typically, the mini-
mum voltage swing the discriminator can see and still fully
1
a
a
b
sin (m(t u) m(t)) .
2
The double frequency component can be filtered off
with a lowpass filter. If u is kept small,
switch is about 100 mV . The two inputs to the discrimina-
PP
1
2
1
2
tor can be of different peak-to-peak voltage swings as long
as both are over the lower limit. This allows the quadrature
tank circuit to have some insertion loss. In fact, up to 8 dB
insertion loss can be tolerated while still ensuring that the
discriminator output won’t suffer.
a
b
&
e
a b
]
m(t u) m(t)
[
sin (m(t u) m(t))
a
t
u
m
2
b
b(t) dt
b(t) dt
b(t) dt
b%
#
t
m
2
(9)
The quadrature circuit can also affect the discriminator out-
put voltage swing. The discriminator output voltage swing
specified assumes perfect quadrature at the frequency of
interest (mixer operation). With available analog compo-
nents, perfect quadrature is not possible. This is due in part
to the high frequency of the IF and the proportionally very
narrow bandwidth of the desired signal. For example, a
b%
a
#
#
t
u
m
2
e
&
t
m
u
b(t) .
2
The object for a delay line, then, is to maximize the de-
lay while retaining the approximations necessary to sat-
isfy (9), u
k
DECT signal is about 1 MHz wide, which is
1% of the IF
at which the demodulation occurs. This makes the quadra-
ture circuit difficult to achieve. With moderately high Q com-
k
0.1 Tb.
ponents, however, a reasonable phase shift can be
achieved with a single pole tank. This is illustrated by the
following equation: the output of the discriminator is given
by
e
a
c
DISC
cos(0 t ) cos(0 t w),
(1)
#
out
c
which results in
e
a
a
a b
cos(0 t 0 t w). (2)
c
b
DISC
cos(0 t 0 t w)
out
c
c
c
When the double frequency component is filtered out with a
low pass filter, the cosine of the phase remains
e
b
e
cos(w).
DISC
cos( w)
(3)
out
It can be seen that at 90 phase shift, the output will be zero.
b
§
At 0 , the output will be 0.5, and at 180 , it will be 0.5. The
§
§
output swing is then set by the multiplication of the cosine
term with the discriminator output amplifier’s gain.
10
11
Physical Dimensions inches (millimeters)
16-Lead Molded Package (SO)
Order Number LMX2240M
For Tape and Reel Order Number LMX2240MX
NS Package Number M16A
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL
SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and whose
failure to perform, when properly used in accordance
with instructions for use provided in the labeling, can
be reasonably expected to result in a significant injury
to the user.
2. A critical component is any component of a life
support device or system whose failure to perform can
be reasonably expected to cause the failure of the life
support device or system, or to affect its safety or
effectiveness.
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Corporation
National Semiconductor
Europe
National Semiconductor
Hong Kong Ltd.
National Semiconductor
Japan Ltd.
a
1111 West Bardin Road
Arlington, TX 76017
Tel: 1(800) 272-9959
Fax: 1(800) 737-7018
Fax:
(
49) 0-180-530 85 86
@
13th Floor, Straight Block,
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Tel: (852) 2737-1600
Fax: (852) 2736-9960
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a
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