Datasheet

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DETAILED DESCRIPTION
Analog Input
Gain Settings for Analog Input
D/A Converter
Common Voltage
Line Output
Headphone Output
Analog Mixing and Bypass
Digital Gain Control
PCM1774
SLAS551 – JULY 2007
The AIN1L and AIN1R pins can be used as microphone or line inputs with selectable 0-, 12-, or 20-dB boost and
1-Vrms input. All of these 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 (AIL0 and AIR0).
The gain of the analog signals can be adjusted from 0 dB to –21 dB in 1-dB steps following the 0-, 12-, or 20-dB
boost amplifier. The gain level can be set for each channel by registers 89 (GMR[2:0], GML [2:0].
The DAC includes a multilevel delta-sigma modulator and an interpolation filter. These can be used to obtain
high PSRR, low jitter sensitivity, and low out-of-band noise quickly and easily. The interpolation filter includes
digital attenuator, digital soft mute, three-band tone control (bass, midrange and treble), and 3-D sound
controlled by registers 92 to 95. The de-emphasis filter (32, 44.1 and 48 kHz) is controlled by registers 68 to 70
(ATL[5:0], ATR[5:0], PMUL, PMUR, DEM[1:0]). Oversampling rate control can reduce out-of-band noise when
operating at low sampling rates by using register 70 (OVER).
The V
COM
pin is normally biased to 0.5 V
CC
, and it provides the common voltage to internal circuitry. It is
recommended that a 4.7- μ F capacitor be connected between this pin and AGND to provide clean voltage and
avoid pop noise. The PCM1774 may have a little pop noise on each analog output if a capacitor smaller than
4.7 μ F is used.
The HPOL/LOL and HPOR/LOR pins can drive a 10-k Ω load and be configured by register 74 (HPS[1:0]) as a
monaural single-ended, monaural differential, or stereo single-line output with 1-Vrms output. These outputs
include an analog volume amplifier that can be set from 6 dB to –70 dB and mute in steps of 0.5-, 1-, 2- or 4-dB.
Each output is controlled by registers 64 and 65 (HLV[5:0], HRV[5:0], HMUL, HMUR). No dc blocking capacitor
is required when connecting an external speaker amplifier with monaural differential input. The center voltage is
0.5 V
CC
with zero data input.
The HPOL/LOL and HPOR/LOR pins can be configured as a stereo, monaural, or monaural differential
headphone output by register 74 (HPS[1:0]). These pins have more than 30 or 40 mWrms output power into a
32- or 16- Ω load, either through a dc blocking capacitor or without a capacitor. These outputs include an analog
volume amplifier that can be set from 6 dB to –70 dB in steps of 0.5, 1, 2, or 4 dB. Each is controlled by
registers 64 and 65 (HLV[5:0], HRV[5:0], HMUL, HMUR). The center voltage is 0.5 V
CC
with zero data input.
Mixing amplifiers (MXL, MXR) mix inputs from the AIN pins. The analog inputs are selected by register 87 (AIR0,
AIL0) and can bypass the DAC and connect the mixed signal to the headphone or speaker outputs by register
88 (MXR[2:0], MXL[2:0]). The gain of the analog inputs is controlled by register 89 (GMR[2:0], GML[2:0]). These
functions are suitable for FM radio, headset, and other analog sources without an ADC.
A portable application with small speakers may be require a high sound level when playing back audio data
recorded at low level. Digital gain control (DGC) can be used to amplify the digital input data by 0, 6, 12 or 18 dB
by setting register 70 (SPX[1:0]).
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