双中频（ IF ）模拟前端数字广播 DUAL INTERMEDIATE FREQUENCY IF ANALOG FRONT-END FOR DIGITAL RADIO
The AFE8221 implements the intermediate frequency IF sampling and processing functions of a digital radio receiver system. It is designed to be used with s digital radio baseband processors and AM/FM tuners. The AFE8221 can also be programmed by the baseband processor for use in conventional AM/FM and digital radio. This unit includes two IF inputs with associated filtering and digital processing circuitry.
The receive circuit oversamples the radio tuner IF output to reduce noise and improve dynamic range. The IF analog-to-digital converter ADC oversamples the IF input at rates up to 75 MHz. The AFE8221 then digitally mixes, filters, and decimates the signal to provide I and Q output signals to the baseband processor. A clock oscillator circuit is provided that can be used with an appropriate third-overtone crystal and external tank circuit to generate the sampling clock for the IF ADCs.
The AFE8221 also includes a real-time clock and associated low-power oscillator circuit. Two auxiliary digital-to-analog converters DACs are included for system control functions. An 8-bit auxiliary ADC and input multiplexer MUX can be used for system diagnostic functions. Other features include 12 general-purpose input/output GPIO lines, programmable interrupt generators, and an I2C master for communication between the AFE and the tuners.
The AFE8221 is available in a TQFP-144 20 mm × 20 mm package and uses a 3.3-V and a 1.8-V power supply. An onboard voltage regulator is included to optionally generate the 1.8-V digital supply for the AFE8221.
