TDA7521 is a BiCMOS analog front end for CD applications. Four input signals (AC*, BD*, E* and F*), coming from the pick-up (whose laser diode is driven and controlled by the device itself), are preamplified by a programmable voltage-to-voltage or current-tovoltage stage, depending on the used pick-up. The output signals from the preamplifier stage (AC, BD, E, F and HF, a radio frequency signal obtained by combining the photo-detector outputs as A+B+C+D) are fed to an 8-bit HF ADC (for HF, which carries encoded audio data) and a 6-bit Servo ADC (for AC, BD, E and F, used for focusing, tracking the laser beam and controlling revolution speed). All these signals are digitized, multiplexed, synchronized with the external clock (768×Fs or 394×Fs, Fs=44.1KHz) and fed to the digital counterpart in one only digital stream (AC/HF/BD/HF/E/HF/F/HF). Two stereo DACs convert the input bitstreams from TDA7522.

All the clock signals (for ADCs and DACs) are generated by a low-jitter PLL-based clock manager. All TDA7521’s analog preprocessing is controlled by TDA7522 by means of an UART interface (which implements an I2C-like protocol). Housed in a TQFP 44, 10×10mm package, TDA7521 features the functions shown in figure below.

TDA7521 uses the HF4CMOS technology and is supplied @5Vdc.