Datasheet

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PCM1870 DESCRIPTION
Analog Input
Gain Setting for Analog Input
A/D Converter
Common Voltage
Microphone Bias
Auto Level Control (ALC) for Recording
3D Sound
3-Band Tone Control
High-Pass Filter and Notch Filter
Digital Monaural Mixing
PCM1870
SLAS544A – MAY 2007 – REVISED SEPTEMBER 2007
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 k Ω ), 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.
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]).
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.
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- μ F capacitor to this pin is recommended to optimize analog performance.
The MICB pin is a microphone bias source for an external microphone, which can provide 2 mA (typ) bias
current.
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.
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.
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.
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.
The audio data can be mixed to monaural digital data from stereo digital data in the internal audio interface
section by register 96 (MXEN).
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