AKM公司的AK4678是24位立体声CODEC,具有内置麦克风放大器,接收放大器,单声道D类扬声器放大器,无电容的G类耳机放大器和线路放大器.除了音频I/F外还有两个PCM I/F.播放功能包括5波段参数EQ和动态范围控制,因此能自动调整合适音量而不失真.本文介绍了AK4678主要特性,模拟和数字方框图,以及评估板 AKD4678-B功能,方框图,电路图和PCB元件布局图.
The AK4678 is a 24bit stereo CODEC with a built-in Microphone-Amplifier, Receiver-Amplifier, Mono Class-D Speaker-Amplifier, Cap-less Class-G Headphone-Amplifier and Line-Amplifier. The AK4678 features dual PCM I/F in addition to audio I/F that allows easy interfacing in mobile phone designs with Bluetooth I/F. The playback features also include 5-band Parametric EQ and Dynamic Range Control, therefore the AK4678 can automatically adjust a comfortable volume without distortion and provides great flexibility. The AK4678 is available in a 49pin CSP, utilizing less board space than competitive offerings.

AK4678主要特性:
1. Recording Function (Stereo CODEC)
• 4 Stereo Input Selectors
• 4 Stereo Inputs (Single-ended) or 3 Mono Input (Full-differential)
• MIC Amplifier: +24dB ~ −6dB, 3dB step
• 2 Output MIC Power Supplies
• Digital ALC (Automatic Level Control): +36dB ~ −54dB, 0.375dB Step, Mute
• ADC CHARACTERISTICS: S/(N+D): 80dB, DR, S/N: 87dB (MIC-Amp=+18dB)S/(N+D): 80dB, DR, S/N: 92dB (MIC-Amp=0dB)
• Stereo Digital MIC Interface
• Wind-noise Reduction Filter
• Stereo Separation Emphasis
• 3-band Programmable Notch Filter
• Audio Interface Format: 24/16bit MSB justified, 24/16bit I2S, 16bit DSP Mode 2. Playback Function (Stereo CODEC)
• Digital Volume (+6dB ~ −57.0dB, 0.5dB Step, Mute)
• Digital ALC (Automatic Level Control): +36dB ~ −54dB, 0.375dB Step, Mute
• Stereo Separation Emphasis
• Dynamic Range Control
• 5-band Parametric Equalizer
• Stereo Line Output (Selectable Full-differential / Single-ended)
• Mono Receiver-Amp
- BTL Output
- Output Power: 60mW @ 32Ω
- Analog Volume: +12 ~ −30dB & Mute, 3dB Step
• Cap-less Stereo Class-G Headphone-Amp
- Output Power: 25mW @ 32Ω, 45mW @ 16Ω
- Analog Volume: +6 ~ −62dB & Mute, 2dB Step
- Zero crossing Detection
- Pop Noise Free at Power-ON/OFF
• Mono Class-D Speaker-Amp
- BTL Output
- Short Protection Circuit
- Output Power: 1.1W @ 8Ω, SVDD=4.2V, THD+N = 10%
 0.89W @ 8Ω, SVDD=4.2V, THD+N = 1%
- Analog Volume: +12 ~ −30dB & Mute, 3dB Step
- Pop Noise Free at Power-ON/OFF
• Audio Interface Format:
- 24/16bit MSB justified, 16bit LSB justified, 16/24bit I2S, 16bit DSP Mode
3. Dual PCM I/F for Baseband & Bluetooth Interface • Four sample Rate Converters (Up sample: up to x6: Down sample: down to x1/6)
• Sample Rate:
- PORTA (Mono): 8 ~ 16kHz
- PORTB (Stereo): 8 ~ 48kHz
• Digital Volume
• Slave Mode
• Audio Interface Format:
- 16bit Linear, 8bit A-law, 8bit μ-law
- Short/Long Frame, I2S, MSB justified
4. Power Management
5. Master Clock(Audio I/F):
(1) PLL Mode
•Frequencies: 11.2896MHz, 12MHz, 12.288MHz, 13MHz, 13.5MHz, 19.2MHz, 24MHz, 25MHz, 26MHz, 27MHz (MCKI pin)
32fs or 64fs (BICK pin)
(2) External Clock Mode
•Frequencies: 256fs, 512fs or 1024fs (MCKI pin)
6. Output Master Clock Frequencies(Audio I/F): 32fs/64fs/128fs/256fs
7. Sampling Frequency (Audio I/F)
•PLL Slave Mode (BICK pin): 8kHz ~ 48kHz
•PLL Master Mode:
8kHz, 11.025kHz, 12kHz, 16kHz, 22.05kHz, 24kHz, 32kHz, 44.1kHz, 48kHz
•EXT Master/Slave Mode:
8kHz ∼48kHz (256fs), 8kHz ~ 24kHz (512fs), 8kHz ~ 12kHz (1024fs)
8. Audio I/F: Master/Slave mode
9. μP I/F: I2C Bus (Ver 1.0, 400kHz Fast Mode)
10. Ta = −30 ~ 85?C
11. Power Supply:
•SVDD (SPK/RCV/LINE-Amp): 3.0 ~ 5.5V
•AVDD (Analog): 1.7 ~ 2.0V
•DVDD (Digital Core): 1.7 ~ 2.0V
•PVDD (HP-Amp & Charge Pump): 1.7 ~ 2.0V
•TVDD (Digital I/F): 1.6 ~ 3.6V
12. Package : 49pin CSP(2.96 x 2.96 mm, 0.4mm pitch)

图1.AK4678模拟方框图

图2.AK4678数字方框图
 
图3.AK4678典型连接图(电源部分)

AK4678评估板 AKD4678-B(Rev.1)
The AKD4678-B is an evaluation board for AK4678, 24bit stereo CODEC with Microphone/Receiver/Headphone/ Speaker/ Line amplifier. The AKD4678-B has the Digital Audio I/F and can achieve the interface with digital audio systems via optical connector.

评估板 AKD4678-B功能:
• DIR/DIT with optical input/output
• 10pin Header for Digital Audio I/F and PCM I/F (Baseband, Bluetooth)
• 10pin Header for I2C control mode

图4.评估板AKD4678-B方框图

图5.评估板AKD4678-B电路图(1)

图6.评估板AKD4678-B电路图(2)

图7.评估板AKD4678-B电路图(3)

图8.评估板AKD4678-B元件布局图