AKM公司的AK7757是一款內置4通道DAC、一個可選輸入立體聲ADC通道、一個單聲道ADC和一個數字音頻接口的數字音頻信號處理器。該音頻數字信號處理器具有在48kHz的采樣速率下達到1536階的并行算法操作性能。本文詳細介紹了AK7757的主要特性、內部框圖、內部DSP框圖以及采用AK7757芯片設計的評估開發板，通過評估板詳細介紹了AK7757芯片各種模式下的應用設置及測試，評估板主要有評估板框圖、電路原理圖。

The AK7757 is a digital signal processor with an integrated 4ch DAC, a stereo ADC with input selector, a mono ADC and an integrated digital audio interface. The audio DSP has 1536 step/fs (at 48kHz sampling) parallel arithmetic operation performance. As the AK7757 is a RAM based DSP, it is programmable for user requirements to realize the audio effects process or the proprietary high-performance HF. It is housed in a 48pin LQFP which is a small package to save the PCB space.

AK7757主要特性

??DSP
- Word length: 24bits (Data RAM: F24 floating point)
- Processing Speed: 13.6 ns (9216step/fs; fs = 8kHz)
- Multiplication: 20 x 20 → 36-bit Double precision arithmetic available
- Divider 20 / 20 → 20-bit
- ALU: 40-bit arithmetic operation (overflow margin 4bits) 24-bit floating point arithmetic and logic operation
- Program RAM: 4096 x 36bits
- Coefficient RAM: 4096 x 20bits
- Data RAM: 2048 x 24bits (F24 floating point)
- Delay RAM: 4096 x 20bits, 4096 x 20bits
- Master Clock: 73.7MHz
- JX pins (interrupt)
??2ch ADC1
- Sampling Frequency: 8kHz~48kHz
- 3in / 1out Input Selector (Diffrentialx1 single endx1 single end with MicAmpx1)
- ADC S/N: 96dBA, S/ (N+D): 88dB
??1ch ADC2
- Sampling Frequency: 8kHz~48kHz
- ADC S/N: 89dBA, S/(N+D): 82dB
??4ch DAC
- Sampling Frequency: 8kHz~48kHz
- DAC S/N: 107dBA, S/ (N+D): 92dB
??Microphone Interface
- Differential or single-end input
- Programmable Gain (+33dB ~ +15dB and 0dB, 3dB step)
- Low Noise Microphone Bias
??Automatic Power Down (CODEC, DSP)
??μP I/F: SPI, I2C
??Power supply
Analog (AVDD): 3.0V ~ 3.6V (typ.3.3V)
Digital1 (DVDD): 3.0V ~ 3.6V (typ.3.3V)
Digital2 (DVDD18): 1.7V ~ 1.9V (typ.1.8V)
??Operating temperature range: -40℃ ~ 85℃
??Package: 48pin LQFP


圖1.內部框圖

圖2.內部DSP框圖

采用AK7757評估板參考設計

The AKD7757-A is an evaluation board for AK7757, which is a highly integrated digital signal processor with an integrated 4ch DAC, a stereo ADC with input selector, a mono ADC and an integrated digital audio interface. This board is composed of a main board and a sub board. The AKD7757-A can be set-up by a PC via USB port. RCA connector is used for both input and output of the analog signal. Digital audio interfaces are also integrated, enabling to Interface with a digital audio system via optical connectors or SMUX-PORTs.

AK7757評估板參考設計的主要特性

??Read/Write access to PRAM, CRAM, OFREG and registers of the AK7757
??Compatible with 2 types of digital audio interface
- Optical input (x1) / Optical output (x1)
- 10pin header for interface with external data source (x2)
??ADC1 6ch input (differential input 3ch, single-end input 3ch), ADC2 1ch input, DAC 4ch output
??USB port for board control


圖3.參考設計框圖


圖4.參考設計原理圖（1）

圖5.參考設計原理圖（2）

圖6.參考設計原理圖（3）

圖7.參考設計原理圖（4）

圖8.參考設計原理圖（5）

圖9.參考設計原理圖（5）

圖10.參考設計原理圖（6）

圖11.參考設計原理圖（7）

圖12.參考設計原理圖（8）

圖13.參考設計原理圖（9）