AKM公司的 AK4955是集成了麦克风放大器，扬声器放大器，视频放大器，LCD和DSP的 24位立体声CODEC，具有录音功能，播放功能，电源管理以及主从模式，主要用在带录音/播放功能的手提设备。本文介绍了AK4955主要特性，方框图以及AKD4955-A评估板方框图，电路图和PCB布局图。
The AK4955 is a 24bit stereo CODEC with a microphone amplifier, speaker amplifier, video amplifier, LDO, and DSP. The input circuits include a microphone amplifier and the output circuits include a speaker amplifier. It is suitable for portable application with recording/playback function. A one channel composite In/Out video amplifier is also integrated. The internal charge pump generates a negative power eliminating the need for AC-coupling capacitors. The AK4955 is available in a small 36pin CSP (3.0mm 3.1mm, 0.5mm pitch), saving mounting area on the board.
Applications: DSCs, DVCs

AK4955主要特性：
Recording Functions
· Stereo Single-ended input with two Selectors
· MIC Amplifier (+24dB/+21dB/+18dB/+16dB/+14dB/+11dB/+8dB/+5dB/0dB)
· Digital ALC (Automatic Level Control) (Setting Range: +36dB ~ -54dB, 0.375dB Step)
· ADC Performance: S/(N+D): 81dB, DR, S/N: 88dB (MIC-Amp=+18dB)S/(N+D): 82dB, DR, S/N: 96dB (MIC-Amp=0dB)
· 5 Band Notch Filter
· Digital MIC Interface
Playback Functions
· Digital De-emphasis Filter (tc=50/15s, fs=32kHz, 44.1kHz, 48kHz)
· Soft Mute
· Digital ALC (Automatic Level Control)(Setting Range: +36dB ~ -54dB, 0.375dB Step)
· Digital Volume Control (+12dB ~ -115dB, 0.5dB Step, Mute)
· Stereo Emphasis Circuit
· Stereo Line Output
Output Voltage: +2dBV(1.26Vrms) (LVDD = 4.8V)2.52Vpp (LVDD=3.3V)
-S/(N+D): 85dB, S/N: 92dB
· Mono Mixing Output
· Mono Speaker-Amplifier
SPK-Amp Performance: S/(N+D): 70dB@150mW, 60dB@250mW, S/N: 95dB
- BTL Output
- Output Power: 600mW@8 (SVDD=4.8V)
400mW@8 (SVDD=3.3V)
· Analog Mixing: Mono Input
· Beep Sound
Power Management
· Thermal Shut-down Function
Master Clock:
(1) PLL Mode
· Frequencies: 11.2896MHz, 12MHz, 13.5MHz, 24MHz, 27MHz (MCKI pin) 32fs or 64fs (BICK pin)
(2) External Clock Mode
· Frequencies: 256fs, 512fs or 1024fs (MCKI pin)
Output Master Clock Frequencies: 32fs/64fs/128fs/256fs
Sampling Frequency
· PLL Slave Mode (BICK pin): 7.35kHz ~ 48kHz
· PLL Slave Mode (MCKI pin): 8kHz, 11.025kHz, 12kHz, 16kHz, 22.05kHz, 24kHz, 32kHz, 44.1kHz, 48kHz
· PLL Master Mode: 8kHz, 11.025kHz, 12kHz, 16kHz, 22.05kHz, 24kHz, 32kHz, 44.1kHz, 48kHz
· EXT Master/Slave Mode: 7.35kHz ~ 48kHz (256fs, 512fs), 7.35kHz ~ 13kHz (1024fs) P I/F: 3-wire Serial, I²C Bus (Ver 1.0, 400kHz Fast-Mode)
Master/Slave mode
Audio Interface Format: MSB First, 2’s complement
· ADC: 24bit MSB justified, 16/24bit I²S
· DAC: 24bit MSB justified, 16bit LSB justified, 24bit LSB justified, 16/24bit I²S
Video Functions
· One Composite Signal Input
· Capacitor-less Video Amplifier for Composite Signal Output Gain: +6 / +9 / +12 / +16.5dB
· LPF
· Charge Pump Circuit for Negative Power Supply
Ta = -30 ~ 85℃
Power Supply:
· Analog Power Supply (AVDD): 2.7 ~ 3.6V
· Digital Power Supply (DVDD): 1.6 ~ 2.0V
· Line Output Power Supply (LVDD): 2.7 ~ 5.5V
· Speaker Power Supply (SVDD): 2.7 ~ 5.5V
· Digital I/O Power Supply (TVDD): -0.2 ~ 3.6V
Package: 36pin QFN (3.0 3.1mm, 0.5mm pitch)
Evaluation Board: AKD4955

图1。AK4955方框图

AKD4955-A评估板
The AKD4955-A is an evaluation board for AK4955, 24bit stereo CODEC with a microphone/ speaker/ video amplifiers, DSP and LDO. The AKD4955-A has the Digital Audio I/F and can achieve the interface with digital audio systems via optical connector.

图2。AKD4955-A评估板方框图

图3。AKD4955-A评估板电路图（1）

图4。AKD4955-A评估板电路图（2）

图5。AKD4955-A评估板电路图（3）

图6。AKD4955-A评估板电路图（4）

图7。AKD4955-A评估板电路图（5）

图8。AKD4955-A评估板电路图（6）

图9。AKD4955-A评估板电路图（7）

图10。AKD4955-A评估板PCB布局图