RF COMMUNICATIONS PRODUCTS
SA625
High performance low power mixer FM IF
system with high-speed RSSI
Product specification
Replaces data of November 3, 1992
IC17 Data Handbook
1997 Nov 07
Philips Semiconductors
Philips Semiconductors
Product specification
High performance low power mixer FM IF system
with high-speed RSSI
SA625
DESCRIPTION
The SA625 is pin-to-pin compatible with the SA605, but has faster
RSSI rise and fall times. The SA625 is a high performance
monolithic low-power FM IF system incorporating a mixer/oscillator,
two limiting intermediate frequency amplifiers, quadrature detector,
muting, logarithmic received signal strength indicator (RSSI) with
fast rise and fall time, and voltage regulator. The SA625 combines
the functions of Signetics’ SA602A and SA624. The SA625 is
available in 20-lead SSOP (shrink small outline package).
For additional technical information please refer to application notes
AN1994, 1995 and 1996, which include example application
diagrams, a complete overview of the product and artwork for
reference.
PIN CONFIGURATION
DK Package
RF
IN
1
20 MIXER OUT
19 IF AMP DECOUPLING
18 IF AMP IN
17
IF AMP DECOUPLING
RF BYPASS 2
XTAL OSC
XTAL OSC
MUTE
IN
V
CC
RSSI
OUT
3
4
5
6
7
16 IF AMP OUT
15 GND
14 LIMITER IN
13
12
11
LIMITER DECOUPLING
LIMITER DECOUPLING
LIMITER OUT
FEATURES
MUTED AUDIO OUT 8
UNMUTED AUDIO OUT 9
QUADRATURE IN 10
•
Fast RSSI rise and fall times
•
Low power consumption: 5.8mA typical at 6V
•
Mixer input to >500MHz
•
Mixer conversion power gain of 13dB at 45MHz
•
Mixer noise figure of 4.6dB at 45MHz
•
XTAL oscillator effective to 150MHz (L.C. oscillator to 1GHz local
oscillator can be injected)
SR00456
•
ESD hardened
Figure 1. Pin Configuration
APPLICATIONS
•
102dB of IF Amp/Limiter gain
•
25MHz limiter small signal bandwidth
•
Temperature compensated logarithmic Received Signal Strength
Indicator (RSSI) with a dynamic range in excess of 90dB
•
Two audio outputs - muted and unmuted
•
Low external component count; suitable for crystal/ceramic/LC
filters
•
Excellent sensitivity:
0.22µV into 50Ω matching network for 12dB
SINAD (Signal to Noise and Distortion ratio) for 1kHz tone with RF
at 45MHz and IF at 455kHz
•
SA625 meets cellular radio specifications
ORDERING INFORMATION
DESCRIPTION
20-Pin Plastic Shrink Small Outline Package (SSOP) (Surface-mount)
•
Digital cellular base stations
•
High performance communications receivers
•
Single conversion VHF/UHF receivers
•
SCA receivers
•
RF level meter
•
Spectrum analyzer
•
Instrumentation
•
FSK and ASK data receivers
•
Log amps
•
Wideband low current amplification
•
Digital cordless telephones
TEMPERATURE RANGE
-40 to +85°C
ORDER CODE
SA625DK
DWG #
SOT266-1
1997 Nov 07
2
853-1648 18664
Philips Semiconductors
Product specification
High performance low power mixer FM IF system
with high-speed RSSI
SA625
BLOCK DIAGRAM
20
19
18
17
16
15
14
13
12
11
IF
AMP
LIMITER
RSSI
OSCILLATOR
E
B
1
2
3
4
5
6
7
8
9
10
SR00457
Figure 2. Block Diagram
ABSOLUTE MAXIMUM RATINGS
SYMBOL
V
CC
T
STG
T
A
θ
JA
Single supply voltage
Storage temperature range
Operating ambient temperature range SA625
Thermal impedance
DK package
PARAMETER
RATING
9
-65 to +150
-40 to +85
117
UNITS
V
°
C
°
C
°
C/W
DC ELECTRICAL CHARACTERISTICS
V
CC
= +6V, T
A
= 25
°
C; unless otherwise stated.
LIMITS
SYMBOL
PARAMETER
TEST CONDITIONS
MIN
V
CC
I
CC
Power supply voltage range
DC current drain
Mute switch input threshold
(ON)
(OFF)
4.5
4.55
1.7
1.0
5.8
SA625
TYP
MAX
8.0
6.75
V
mA
V
V
UNITS
1997 Nov 07
3
Philips Semiconductors
Product specification
High performance low power mixer FM IF system
with high-speed RSSI
SA625
level = -45dBm; FM modulation = 1kHz with
±8kHz
peak deviation. Audio output with C-message weighted filter and de-emphasis capacitor.
Test circuit Figure 3. The parameters listed below are tested using automatic test equipment to assure consistent electrical characterristics.
The limits do not represent the ultimate performance limits of the device. Use of an optimized RF layout will improve many of the listed parame-
ters.
LIMITS
SYMBOL
PARAMETER
TEST CONDITIONS
MIN
Mixer/Osc section (ext LO = 300mV)
f
IN
f
OSC
Input signal frequency
Crystal oscillator frequency
Noise figure at 45MHz
Third-order input intercept point
Conversion power gain
RF input resistance
RF input capacitance
Mixer output resistance
IF section
IF amp gain
Limiter gain
Input limiting -3dB, R
17
= 5.1k
AM rejection
Audio level, R
10
= 100k
Unmuted audio level, R
11
= 100k
SINAD sensitivity
THD
S/N
Total harmonic distortion
Signal-to-noise ratio
IF RSSI output, R
9
=
100kΩ
1
No modulation for noise
IF level = -118dBm
IF level = -68dBm
IF level = -18dBm
IF frequency = 455kHz
RF level = -56dBm
IF RSSI output rise time
(10kHz pulse, no 455kHz filter)
(no RSSI bypass capacitor)
RF level = -28dBm
IF frequency = 10.7MHz
RF level = -56dBm
RF level = -28dBm
IF frequency = 455kHz
RF level = -56dBm
IF RSSI output fall time
(10kHz pulse, no 455kHz filter)
(no RSSI bypass capacitor)
RSSI range
RSSI accuracy
IF input impedance
IF output impedance
Limiter intput impedance
Limiter output impedance
Limiter output level with no load
RF level = -28dBm
IF frequency = 10.7MHz
RF level = -56dBm
RF level = -28dBm
R
9
= 100kΩ Pin 16
R
9
= 100kΩ Pin 16
1.40
0.85
1.40
2.0
7.3
90
+1.5
1.6
1.0
1.6
300
280
µs
µs
dB
dB
kΩ
kΩ
kΩ
Ω
mV
RMS
2.1
7.6
µs
µs
1.2
1.1
µs
µs
1.2
1.2
µs
µs
0
1.9
4.0
50Ω source
50Ω source
Test at Pin 18
80% AM 1kHz
15nF de-emphasis
150pF de-emphasis
RF level -118dB
-34
29
80
39.7
62.5
-113
34
150
480
16
-42
73
160
2.5
4.8
650
3.1
5.6
43
260
dB
dB
dBm
dB
mV
RMS
mV
dB
dB
dB
mV
V
V
(Pin 20)
1.25
f1 = 45.0; f2 = 45.06MHz
Matched 14.5dBV step-up
50Ω source
Single-ended input
3.0
10
500
150
5.0
-10
13
-1.7
4.7
3.5
1.5
4.0
15
MHz
MHz
dB
dBm
dB
dB
kΩ
pF
kΩ
SA625
TYP
MAX
UNITS
AC ELECTRICAL CHARACTERISTICS
T
A
= 25
°
C; V
CC
= +6V, unless otherwise stated. RF frequency = 45MHz + 14.5dBV RF input step-up; IF frequency = 455kHz; R17 = 5.1k; RF
1997 Nov 07
4
Philips Semiconductors
Product specification
High performance low power mixer FM IF system
with high-speed RSSI
SA625
AC ELECTRICAL CHARACTERISTICS
(Continued)
LIMITS
SYMBOL
IF section
(continued)
Unmuted audio output resistance
Muted audio output resistance
RF/IF section (int LO)
Unmuted audio level
System RSSI output
4.5V = V
CC
, RF level = -27dBm
4.5V = V
CC
, RF level = -27dBm
450
4.3
mV
RMS
V
58
58
kΩ
kΩ
PARAMETER
TEST CONDITIONS
MIN
SA625
TYP
MAX
UNITS
NOTE:
1. The generator source impedance is 50Ω, but the SA625 input impedance at Pin 18 is 1500Ω. As a result, IF level refers to the actual signal
that enters the SA625 input (Pin 8) which is about 21dB less than the ”available power” at the generator.
CIRCUIT DESCRIPTION
The SA625 is an IF signal processing system suitable for second IF
or single conversion systems with input frequency as high as 1GHz.
The bandwidth of the IF amplifier is about 40MHz, with 39.7dB(v) of
gain from a 50Ω source. The bandwidth of the limiter is about
28MHz with about 62.5dB(v) of gain from a 50Ω source. However,
the gain/bandwidth distribution is optimized for 455kHz, 1.5kΩ
source applications. The overall system is well-suited to battery
operation as well as high performance and high quality products of
all types.
The input stage is a Gilbert cell mixer with oscillator. Typical mixer
characteristics include a noise figure of 5dB, conversion gain of
13dB, and input third-order intercept of -10dBm. The oscillator will
operate in excess of 1GHz in L/C tank configurations. Hartley or
Colpitts circuits can be used up to 100MHz for xtal configurations.
Butler oscillators are recommended for xtal configurations up to
150MHz.
The output of the mixer is internally loaded with a 1.5kΩ resistor
permitting direct connection to a 455kHz ceramic filter. The input
resistance of the limiting IF amplifiers is also 1.5kΩ. With most
455kHz ceramic filters and many crystal filters, no impedance
matching network is necessary. To achieve optimum linearity of the
log signal strength indicator, there must be a 12dB(v) insertion loss
between the first and second IF stages. If the IF filter or interstage
network does not cause 12dB(v) insertion loss, a fixed or variable
resistor can be added between the first IF output (Pin 16) and the
interstage network.
The signal from the second limiting amplifier goes to a Gilbert cell
quadrature detector. One port of the Gilbert cell is internally driven
by the IF. The other output of the IF is AC-coupled to a tuned
quadrature network. This signal, which now has a 90
°
phase
relationship to the internal signal, drives the other port of the
multiplier cell.
Overall, the IF section has a gain of 90dB. For operation at
intermediate frequencies greater than 455kHz, special care must be
given to layout, termination, and interstage loss to avoid instability.
The demodulated output of the quadrature detector is available at
two pins, one continuous and one with a mute switch. Signal
attenuation with the mute activated is greater than 60dB. The mute
input is very high impedance and is compatible with CMOS or TTL
levels.
A log signal strength completes the circuitry. The output range is
greater than 90dB and is temperature compensated. This log signal
strength indicator exceeds the criteria for AMPs or TACs cellular
telephone.
NOTE: dB(v) = 20log V
OUT
/V
IN
1997 Nov 07
5
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