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
