關鍵詞： AK4955 , AKM , Codec , 立體聲 , 錄音播放

AKM公司的 AK4955是集成了麥克風放大器，揚聲器放大器，視頻放大器，LCD和DSP的 24位立體聲CODEC，具有錄音功能，播放功能，電源管理以及主從模式，主要用在帶錄音/播放功能的手提設備。本文介紹了AK4955主要特性，方框圖以及AKD4955-A評估板方框圖，電路圖和PCB布局圖。

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