Philips Semiconductors RF Communications Products
Product specification
Low-voltage digital IF receiver
SA637
DESCRIPTION
The SA637 is a low-voltage high performance
monolithic digital system with high-speed
RSSI incorporating a mixer, oscillator with
buffered output, two limiting intermediate
frequency amplifiers, fast logarithmic
received signal strength indicator (RSSI),
voltage regulator, RSSI op amp and power
down pin. The SA637 is available in SSOP
(shrink small outline package).
The SA637 was designed for portable digital
communication applications and will function
down to 2.7V. The limiter amplifier has
differential outputs with 2MHz small signal
bandwidth. The RSSI output has access to
the feedback pin. This enables the designer
to level adjust the outputs or add filtering.
FEATURES
•
V
CC
= 2.7 to 5.5V
•
Low power receiver (3.8mA @ 3V)
•
Power down mode (I
CC
= 110µA)
•
Fast RSSI rise and fall times
•
Extended RSSI range with temperature
compensation
PIN CONFIGURATION
DK Packages
RF
IN
1
RF
IN
2
OSC E 3
OSC B 4
OSC 5
BUFFER
6
V
20 MIXER
OUTPUT
19 IF AMP
DECOUP
18 IF AMP IN
17 IF AMP
DECOUP
16 IF AMP OUT
15 GND
14 LIMITER IN
13 LIMITER
DECOUP
12 LIMITER
DECOUP
11 LIM OUT (+)
•
RSSI op amp
•
2MHz limiter small signal bandwidth
•
455kHz filter matching (1.5kΩ)
•
Differential limiter output
•
Oscillator buffer
•
SSOP-20 package
APPLICATIONS
CC
RSSI 7
RSSI 8
FEEDBACK
POWER 9
DOWN
LIM OUT (-) 10
•
ADC (American Digital Cellular)
•
Digital receiver systems
•
Cellular radio
ORDERING INFORMATION
DESCRIPTION
20-Pin Plastic Shrink Small Outline Package (Surface-mount)
TEMPERATURE RANGE
-40 to +85°C
ORDER CODE
SA637DK
DWG #
1563
BLOCK DIAGRAM
20
19
18
17
16
15
14
13
12
11
GND
IF
AMP
MIXER
LIMITER
OSCILLATOR
FAST RSSI
+ –
+
–
E
1
2
3
4
B
5
V
CC
6
7
8
POWER
DOWN
9
10
October 27, 1993
2
853-1718 11205
Philips Semiconductors RF Communications Products
Product specification
Low-voltage digital IF receiver
SA637
ABSOLUTE MAXIMUM RATINGS
SYMBOL
V
CC
V
IN
T
STG
T
A
Supply voltage
Voltage applied to any other pin
Storage temperature range
Operating ambient temperature range
PARAMETER
RATING
-0.3 to +6.0
-0.3 to (V
CC
+ 0.3)
-65 to +150
-40 to +85
UNITS
V
V
NOTE:
Thermal impedance (θ
JA
) = 117
°
C/W
°
C
°
C
DC ELECTRICAL CHARACTERISTICS
V
CC
= +3V, T
A
= 25
°
C; unless otherwise stated.
SYMBOL
V
CC
I
CC
PARAMETER
Power supply voltage range
DC current drain
Standby
Input current
Input level
t
ON
t
OFF
Power up time
Power down time
Pin 9 = HIGH or OPEN
V
CC
= 4.7V
Pin 9 = LOW
Pin 9 = LOW
Pin 9 = HIGH
Pin 9 = LOW
Pin 9 = HIGH
RSSI valid (10% to 90%)
RSSI invalid (90% to 10%)
-10
-10
0
0.7V
CC
10
5
TEST CONDITIONS
MIN
2.7
3.8
4.4
0.11
LIMITS
TYP
MAX
5.5
4.5
5.5
0.5
10
10
0.3V
CC
V
CC
V
mA
mA
mA
µA
µA
µA
µA
µs
µs
UNITS
AC ELECTRICAL CHARACTERISTICS
T
A
= 25
°
C; V
CC
= +3V, unless otherwise stated. RF frequency = 90MHz; RF input step-up = +14.5dBV; IF frequency = 455kHz; RF level =
-68dBm. Test circuit Figure 1. The parameters listed below are tested using automatic test equipment to assure consistent electrical
characteristics. The limits do not represent the ultimate performance limits of the device. Use of an optimized RF layout will improve many of
the listed parameters.
SYMBOL
Mixer/Osc section
f
IN
f
OSC
NF
TOI
P1dB
R
IN
C
IN
R
OUT
IF section
IF amp power gain
Limiter power gain
IF
BW
IF amp bandwidth
50Ω source
50Ω source
36
60
2.5
dB
dB
MHz
Input signal frequency
Crystal oscillator frequency
Noise figure at 90MHz
Third-order input intercept point
Input 1dB compression point
Conversion power gain
Mixer input resistance
Mixer input capacitance
Mixer output resistance
Buffered LO output level
LO = 447mV
P-P
, 1kΩ AC load
100
Matched 50Ω
Matched input and output
Input matched to 50Ω source
200
200
6.2
-17
-27
7
2.5
2.2
1.87
300
500
MHz
MHz
dB
dBm
dBm
dB
kΩ
pF
kΩ
mV
P-P
PARAMETER
TEST CONDITIONS
MIN
LIMITS
TYP
MAX
UNITS
October 27, 1993
3
Philips Semiconductors RF Communications Products
Product specification
Low-voltage digital IF receiver
SA637
AC ELECTRICAL CHARACTERISTICS
(Continued)
SYMBOL
PARAMETER
RF RSSI output
TEST CONDITIONS
MIN
RF level = -118dBm
RF level = -68dBm
RF level = -28dBm
RSSI range
RSSI accuracy
RSSI ripple
RSSI speed
Rise time
RSSI speed
Fall time
IF input impedance
IF output impedance
Limiter input impedance
Limiter output impedance
Limiter output signal level
Limiter output DC level
Differential output matching
Differential output offset
(Pin 10, Pin 11)
(Pin 10, Pin 11) 1.5kΩ AC load
No interstage filter
With interstage filter
10
50
1.5
1.5
1.5
200
280
1.27
±6
±30
overall bandwidth is limited to 2MHz. The
input and output impedance of the IF
amplifier and the input impedance of the IF
limiter are set to 1500Ω (match to 455kHz
filter). A second filter is connected between
the IF amplifier and the limiter for improved
channel selectivity and reduced instability.
This ceramic filter provides 3dB interstage
insertion loss which results in optimal RSSI
linearity. The overall gain can be reduced if
desired by adding an external attenuator after
the IF amplifier. The differential limiter
outputs (Pins 10 and 11) are available for
demodulator circuits.
µs
µs
kΩ
kΩ
kΩ
Ω
mV
P-P
V
mV
mV
No interstage filter
With interstage filter
2.5
22
µs
µs
.01
.4
1.0
LIMITS
TYP
0.2
0.9
1.7
90
±1.5
30
MAX
.65
1.7
2.3
V
V
V
dB
dB
mV
P-P
UNITS
CIRCUIT DESCRIPTION
Mixer
The mixer has a balanced input and is
capable of being driven single-ended. The
input impedance is 2.5kΩ in parallel with a
2.2pF cap at 90MHz RF. The mixer output
can drive a 1500Ω ceramic filter at 455kHz or
600kHz directly without any matching
required. The mixer conversion power gain is
7dB when both input and output are matched
and optimum LO level is used to drive the
internal mixer core.
bandwidth of the external bandpass filter that
is placed between the mixer and the IF, and
the external filter placed between the IF
amplifier and limiter. Since the RSSI function
requires the signal to propagate through the
whole IF strip, and the rise and fall time of the
filters are inversely proportional to their
bandwidth, there is a trade-off between
channel selectivity and RSSI response. A
possible solution is to use a second SA637
with wider band external filters for faster
RSSI response.
The RSSI curve is temperature compensated
and in addition is designed for improved
consistency from unit to unit.
The RSSI circuit drives an on-chip low power
op amp with rail-to-rail output which can be
connected as a unity gain RSSI buffer or a
gain stage or even a comparator.
Oscillator and Buffer
The on-board oscillator supplies the signal for
the mixer down-conversion. The internally
biased transistor can be configured as a
Colpitts or Butler overtone crystal oscillator.
The transistor’s bias current can be
increased if desired by adding a shunt
resistor from Pin 3 to ground. The oscillator’s
buffered output (Pin 5) can be used as a
feedback signal to lock the oscillator to an
appropriate reference.
RSSI
The received signal strength indicator
provides a linear voltage indication of the
received signal strength in dB for a range in
excess of 90dB. The response time to a
change in input signal is less than a few
microseconds and the delay is kept to a
minimum because of the use of a minimum
phase shift circuit. Because of the speed of
the RSSI circuit, the RSSI rise and fall time
may, in practice, be dominated by the
DC Power Supply
The IC is designed for operation between 2.7
and 5.5V. A power supply dependent biasing
scheme is used in the mixers to benefit from
the large headroom available at higher V
CC
s.
IF Amplifier and IF Limiter
The IF strip provides more than 95dB of
power gain for the down converted signal. Its
October 27, 1993
4
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