AKM公司的AK4688是一款立體聲音頻CODEC。內嵌支持異步操作的24位ADC和DAC輸入/輸出數據接口，通過外部電阻調節預放大器的輸入范圍來支持線路輸入。內部集成一個電荷泵，通過3.3V單電源供電，獲得一個對地2Vrms電源，以減少外部交流耦合電容及抑制電路。AK4688芯片ADC部分動態范圍為99dB，DAC部分動態范圍為105dB。設計方案不僅介紹了AK4688芯片ADC及DCA的特性，而且還介紹了該芯片的異步操作特性。同時，本方案提供了一個S/PDIF接口以方便連接數字音頻設備。本文詳細介紹了AK4688的主要特性、內部框圖、應用框圖以及采用AK4688芯片設計的評估開發板電路原理圖及PCB Layout圖。

The AK4688 is a stereo audio CODEC. The integrated ADC and DAC interfaces accept up to 24-bit input/output data and support an asynchronous operation. The input range of the pre-amplifier, that supports line inputs, is adjustable by an external resistor. A ground referenced 2Vrms output with a 3.3V single power supply is achieved by an integrated charge pump, reducing external parts such as AC-coupling capacitors and mute circuits. The ADC block of the AK4688 achieves a dynamic range of 99dB, and the DAC block achieves a dynamic range of 105dB. The AK4688 is suitable for digital recording systems, digital TVs, Blu-ray recorders and Home theater systems.

AK4688主要特性

??Asynchronous ADC/DAC Operation

??Capless Stereo Pre-amplifier for Line Input/Output

??24bit Stereo ADC

- 64x Oversampling

- Sampling Rate up to 48kHz

- Linear Phase Digital Anti-Alias Filter

- S/(N+D): 83dB

- Dynamic Range, S/N: 99dB

- Digital HPF for Offset Cancellation

??24bit Stereo DAC

- 128x Oversampling

- Sampling Rate up to 192kHz

- 24bit 8 times Digital Filter

- S/(N+D): 95dB

- Dynamic Range, S/N: 105dB

- De-emphasis Filter

??High Jitter Tolerance

??External Master Clock Input:

256fs, 384fs, 512fs 768fs (fs=32kHz ∼ 48kHz)

128fs, 192fs, 256fs 384fs (fs=64kHz ∼ 96kHz)

128fs, 192fs (fs=128kHz ~ 192kHz)

??2 Audio Serial I/F (PORT1, PORT2)

- Master/Slave mode (PORT1)

- I/F format

PORT1, 2: MSB, LSB justified (16/24 bit), I2S

??Hardware / I2C-bus Control

??Operating Voltage:

- Digital I/O and Charge Pump: 3.0V ∼ 3.6V

- ADC Analog: 3.0V ∼ 3.6V

- DAC Analog: 3.0V ∼ 3.6V

??Package: 36pin QFN



圖1.內部框圖

采用AK4688評估板參考設計

AKD4688-A is an evaluation board for AK4688, which is a single chip 24bit CODEC with a 2ch ADC and a 2ch DAC. It is possible to evaluate not only A/D and D/A of the AK4688, but also asynchronous operation characteristics. Also, the board could be connected to a digital’s audio equipment easily with S/PDIF connectors.

AK4688評估板參考設計的主要特性

??Compatible with 2 types of digital audio interface

- Optical (S/PDIF) input/output with DIT/DIR (AK4118A)

- 10pin headers for interfacing with external data source

??Separate power supply or regulator power supply

??10pin header for register control


圖2.參考設計框圖

AK4688評估板原理圖

圖3.參考設計原理圖（1）

圖4.參考設計原理圖（2）

圖5.參考設計原理圖（3）

圖6.參考設計原理圖（4）

圖7.參考設計原理圖（5）

圖8.參考設計原理圖（6）

AK4688評估板PCB Layout圖