SA626 Philips Semiconductors (Acquired by NXP), SA626 Datasheet - Page 7

• Manufacturer Part Number: SA626
• Description: SA626; Low Voltage High Performance Mixer FM if System With High-speed Rssi
• Manufacturer: Philips Semiconductors (Acquired by NXP)

power gain from a 50 source. The bandwidth of the limiter is about
Philips Semiconductors
CIRCUIT DESCRIPTION
The SA626 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 38dB of
28MHz with about 54dB of power gain from a 50 source.
However, the gain/bandwidth distribution is optimized for 10.7MHz,
330 source applications. The overall system is well-suited to
battery operation as well as high performance and high quality
products of all types, such as cordless and cellular hand-held
phones.
The input stage is a Gilbert cell mixer with oscillator. Typical mixer
characteristics include a noise figure of 14dB, conversion power
gain of 11dB, and input third-order intercept of -16dBm. 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 330 resistor
permitting direct connection to a 10.7MHz ceramic filter. The input
resistance of the limiting IF amplifiers is also 330 . With most
10.7MHz 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 3dB insertion loss
1997 Sept 25
Low voltage high performance mixer FM IF system
with high-speed RSSI
SA626 IF Amplifier Gain vs Temperature vs Supply Voltage
50.00
48.00
46.00
44.00
42.00
40.00
38.00
36.00
34.00
32.00
30.00
TEMPERATURE ( C)
V
V
V
CC
CC
CC
Figure 5. Performance Characteristics
= 5V
= 3V
= 2.7V
7
between the first and second IF stages. If the IF filter or interstage
network does not cause 3dB 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 power gain of 92dB. For operation at
intermediate frequency at 10.7MHz. Special care must be given to
layout, termination, and interstage loss to avoid instability.
The demodulated output of the quadrature drives an internal op
amp. This op amp is configured as a unity gain buffer. It can drive
an AC load as low as 5k with a rail-to-rail output.
A log signal strength indicator 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, and RCR-28 cordless telephone. This signal
drives an internal op amp. The op amp is capable of rail-to-rail
output. It can be used for gain, filtering, or 2nd-order temperature
compensation of the RSSI, if needed.
65.00
63.00
61.00
59.00
57.00
55.00
53.00
51.00
49.00
47.00
45.00
SA626 Limiting Amplifier Gain vs Temperature
vs Supply Voltage
TEMPERATURE ( C)
V
V
V
CC
CC
CC
= 5V
= 3V
= 2.7V
Product specification
SA626
SR00474