Circuit structure of audio DA converter

The audio D/A converter is a circuit that converts digital audio signals into analog audio signals. The
digital audio signal output after processing by the data signal processing circuit is the same as the digital signal of the CD laser record player, and is a pulse code modulated digital signal (PCM). . This signal is
composed of three signals and needs to be transmitted simultaneously, namely the serial data signal (SDA) and the serial clock signal (BCK, also called data clock). The other
one is the left and right separated clock signal (LRCK).
    The digital audio signal is converted into channel analog audio signals (L, R) by a D/A converter before it can be sent to headphones or speakers for listening. There are many kinds of integrated circuits for D/A
conversion. MS6313, MS6333, SPCA713A and other circuits are commonly used in MP3/MP4 machines. The main
feature of these circuits is that they can work under low voltage (3.3 V) conditions. The typical structure of
    the audio D/A converter is shown in Figure 21-36. This circuit uses the SPCA713A audio D/A integrated circuit. The audio
digital signals (3 channels) are added to the ①, ⑦, and @ pins of U6 SPCA713A. Digital/． Analog conversion processing, and then the analog audio (L, R) signals
are output from the @ and ⑥ pins respectively , which can be sent to headphones or speakers.