PCM3793A
PCM3794A
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SLAS529A–JANUARY 2007–REVISED FEBRUARY 2007
Speaker Output (Class-D, PCM3793A)
The SPOLP/SPOLN and SPORP/SPORN pins are stereo or mono speaker differential outputs (BTL) pairs with a
maximum of 700 mWrms (VPA = 3.6 V, volume = 6 dB) into an 8-Ω load. The digital speaker amplifier offers
maximum battery life, minimum heat, and elimination of LC low-pass filtering. The speaker amplifier includes an
analog volume control with 6 dB to –70 dB in steps of 0.5, 1, 2 or 4 dB steps for each output, which can be set
by registers 66 (SLV[5:0] and 67 SRV[5:0]). Spectrum spreading technology and selectable switching frequency
to reduce EMI noise are controlled by register 71 (DFQ[2:0], SPS[1:0] and SPSE). This digital amplifier has a
thermal shutdown circuit that detects when the device temperature reaches approximately 150°C; then the
speaker amplifier is shut down.
Analog Mixing and Bypass
Mixing amplifiers (MXL, MXR) mix inputs from the AIN pins. The analog inputs are selected by register 87
(AD2S, AIR[1:0],AIL[1:0]) and can bypass the ADC/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.
Microphone Bias
The MICB pin is the microphone bias source for an external microphone. MICB can provide 2 mA (typical) of
bias current.
Digital Gain Control
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]).
Automatic Level Control (ALC) for Recording
The sound for microphone recording should be expanded to a suitable level without saturation. The digitally
controlled automatic level control (ALC) provides automatic expansion for small input signals and compression
for large input signals while recording. The expansion level, compression level, attack time, and recovery time
can be selected by register 83. The register 83 description explains the details of these settings.
3-D Sound
A 3-D sound effect is provided by mixing L-channel and R-channel data with a band-pass filter with two
parameters, mixing ratio and band pass filter characteristic, that can be controlled by register 95 (3DP[3:0],
3FLO). The 3-D sound effect uses the DAC digital input or ADC digital output selected by register 95 (SDAS).
Three-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 registers 92 to 94 (LGA[4:0], MGA[4:0] and HGA[4:0]). Register 92 (LPAE) attenuates the digital input signal
automatically to prevent clipping of the output signal at settings above 0 dB for bass control. LPAE has no effect
on midrange and treble controls.
High-Pass Filter and Two-Stage Programmable Notch Filter
The high-pass filter eliminates the dc offset of the ADC analog signal and can be set for a cutoff frequency of 4
Hz, 120 Hz, or 240 Hz at the 48-kHz sampling frequency by register 81 (HPF[1:0]). A register 95 (SDAS)
selection applies the filter to either the DAC digital input or the ADC digital output.
Notch filters are provided to remove noise of a particular frequency, such as CCD noise, motor noise, or other
mechanical noise in a particualr application. The PCM3793A/94A has two notch filters for which the center
frequency and frequency bandwidth can be programmed by registers 96 to 104. A register 95 (SDAS) selection
applies the filter to either the DAC digital input or the ADC digital output.
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