DESCRIPTION
The SA1638 is a combined Rx and Tx IF I/Q circuit. The receive path contains an IF amplifier, a pair of quadrature down-mixers, and a pair of baseband filters and amplifiers. A second pair of mixers in the transmit path transposes a quadrature baseband input up to the IF frequency. An external VCO signal is divided down internally and buffered to provide quadrature local oscillator signals for the mixers.

FEATURES
• Direct supply: 3.3V to 7.5V
• Two DC regulators giving 3.0V output
• Low current consumption: 18mA for Rx or 22mA for Tx
• Input/output IF frequency from 70-400 MHz
• Internal IF PLL for synthesizing the local oscillator signal
• High performance on-board integrated receive filters with bandwidth tunable between 50-850 kHz
• Switchable alternative bandwidth setting available to allow channel bandwidth flexibility in operation
• Designed for a widely used I and Q baseband GSM interface
• Control registers power up in a default state
• Optional DC offset trim capability to <200mV
• Only a standard reference input frequency required, choice of 13, 26, 39 or 52MHz
• Fully compatible with SA1620 GSM RF front-end (see Figure 9)

APPLICATIONS
• IF circuitry for GSM 900MHz hand-held units
• IF circuitry for PCN (DCS1800) hand-held units
• Quadrature up and down mixer stage