The SA639 is a low-voltage high performance monolithic FM IF system with high-speed
RSSI incorporating a mixer/oscillator, two wideband limiting intermediate frequency
amplifiers, quadrature detector, logarithmic Received Signal Strength Indicator (RSSI),
fast RSSI op amps, voltage regulator, wideband data output, post detection filter amplifier
and data switch. The SA639 is available in 24-lead TSSOP (Thin Shrink Small Outline
The SA639 was designed for high-bandwidth portable communication applications and
functions down to 2.7 V. The RF section is similar to the famous NE605. The data output
provides a minimum bandwidth of 1 MHz to demodulate wideband data. The RSSI output
is amplified and has access to the feedback pin. This enables the designer to level adjust
the outputs or add filtering.
The post-detection amplifier may be used to realize a low-pass filter function. A
programmable data switch routes a portion of the data signal to an external integration
circuit that generates a data comparator reference voltage.
SA639 incorporates a Power-down mode which powers down the device when pin 8
(POWER_DOWN_CTRL) is HIGH. Power down logic levels are CMOS and TTL
compatible with high input impedance.