PCM1870 Datasheet, PDF (11/49 Pages) Burr-Brown (TI) – 16-Bit Low-Power Stereo Audio ADC With Microphone Bias and Microphone Amplifier

PCM1870
www.ti.com
PCM1870 DESCRIPTION
SLAS544 – MAY 2007
Analog Input
The AIN1L, AIN1R, AIN2L and AIN2R pins can be used as microphone or line inputs with selectable 0- or 20-dB
boost and 1-Vrms input. All analog inputs have high input impedance (20 kΩ), which is not changed by gain
settings. One pair of inputs is selected by register 87 (AIL[1:0], AIR[1:0]). AIN1L and AIN1R can also be used as
a monaural differential input.
Gain Setting for Analog Input
Analog signals can be adjusted from 30 dB to –12 dB in 1-dB steps after the 0-, 12- or 20-dB boost amplifier.
Gain level can be set for each channel by register 79, 80 (ALV[5:0], ARV[5:0]).
A/D Converter
The ADC includes a multilevel delta-sigma modulator, aliasing filter, decimation filter, high-pass filter and notch
filter and can accept 1 Vrms as full-scale input voltage. The decimation filter has a digital soft mute controlled by
register 81 (RMUL, RMUR), and the high-pass and notch filters can be disabled by register 81 (HPF[1:0]) and
registers 96 through 104 if they are not needed to cancel dc offset or avoid wind noise.
Common Voltage
Unbuffered common voltage. The V_COM pin is normally biased to 0.5 V_CC, and it provides common voltage to
internal circuitry. Connecting a 4.7-µF capacitor to this pin is recommended to optimize analog performance.
Microphone Bias
The MICB pin is a microphone bias source for an external microphone, which can provide 2 mA (typ) bias
current.
Auto Level Control (ALC) for Recording
The sound when microphone recording should be adjusted to a suitable level without saturation. The digitally
controlled auto level control (ALC) automatically expands small input signals and compresses large input signals
while recording. Expansion level, compression level, attack time, and recovery time can be selected by register
83. See the bit descriptions of register 83 for detailed settings.
3D Sound
A 3D sound effect is provided by mixing L-channel and R-channel data through a band-pass filter with two
control parameters, mixing ratio and band-pass filter characteristic. The control parameters are set in register 95
(3DP[3:0], 3FLO). The 3D sound effect is applied to the ADC digital output.
3-Band Tone Control
Tone control has bass, midrange, and treble controls that can be adjusted from 12 dB to –12 dB in 1-dB steps
by register 92 to 94 (LGA[4:0], MGA[4:0] and HGA[4:0]). Register 92 (LPAE), which attenuates the digital input
signal automatically, can prevent clipping of the output signal at settings higher than 0 dB for bass control. LPAE
is not effective for midrange and treble control.
High-Pass Filter and Notch Filter
The high-pass filter cuts dc offset in the analog section of the ADC and can be set to 4 Hz, 120 Hz, or 240 Hz at
48-kHz sampling by register 81 (HPF[1:0]).
Notch filters remove noise at particular frequencies, CCD noise, motor noise and other mechanical noise in an
application. The PCM1870 has two notch filters, whose center frequency and frequency bandwidth can be
programmed by registers 96 to 104.
Digital Monaural Mixing
The audio data can be mixed to monaural digital data from stereo digital data in the internal audio interface
section by register 96 (MXEN).
Submit Documentation Feedback
11