SA58641 Philips Semiconductors, SA58641 Datasheet - Page 15

• Manufacturer Part Number: SA58641
• Description: High performance mixer FM IF system
• Manufacturer: Philips Semiconductors

Philips Semiconductors
CIRCUIT DESCRIPTION
The SA58641 is an IF signal processing system suitable for second
IF or single conversion systems with input frequency as high as
1 GHz. The bandwidth of the IF amplifier is about 40 MHz, with
38 dB of gain from a 50
about 28 MHz with about 54 dB of gain from a 50
However, the gain/bandwidth distribution is optimized for 10.7 MHz,
330
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 14 dB, conversion gain of
11 dB, and input third-order intercept of –16 dBm. The oscillator will
operate in excess of 1 GHz in L/C tank configurations. Hartley or
Colpitts circuits can be used up to 100 MHz for xtal configurations.
Butler oscillators are recommended for xtal configurations up to
150 MHz.
The output of the mixer is internally loaded with a 330
permitting direct connection to a 10.7 MHz ceramic filter for
narrowband applications. The input resistance of the limiting IF
amplifiers is also 330 . With most 10.7 MHz ceramic filters and
many crystal filters, no impedance matching network is necessary.
For applications requiring wideband IF filtering, such as DECT,
external LC filters are used (see Figure 10). To achieve optimum
linearity of the log signal strength indicator, there must be a 6 dB(v)
2004 Dec 16
High performance mixer FM IF system
with high-speed RSSI
source applications. The overall system is well-suited to
source. The bandwidth of the limiter is
source.
resistor
15
insertion loss between the first and second IF stages. If the IF filter
or interstage network does not cause 6 dB(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 90 dB. For operation at
intermediate frequency at 10.7 MHz. Special care must be given to
layout, termination, and interstage loss to avoid instability.
The demodulated output (DATA) of the quadrature is a voltage
output. This output is designed to handle a minimum bandwidth of
600 kHz. This is designed to demodulate wideband data, such as in
DECT applications.
A Receive Signal Strength Indicator (RSSI) completes the circuitry.
The output range is greater than 90 dB and is temperature
compensated. This log signal strength indicator exceeds the criteria
for AMPS or TACS cellular telephone, DECT 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.
NOTE: dB(v) = 20log V
OUT
/V
IN
SA58641
Objective data