Datasheet

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HIGH-PASS FILTER (HPF) FREQUENCY RESPONSE
Normalized Frequency − y f
S
/1000
−100
−90
−80
−70
−60
−50
−40
−30
−20
−10
0
0.0 0.1 0.2 0.3 0.4
Amplitude − dB
G028
Normalized Frequency − y f
S
/1000
−1.0
−0.8
−0.6
−0.4
−0.2
0.0
0.2
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Amplitude − dB
G029
PRINCIPLES OF OPERATION
THEORY OF OPERATION
PCM1804
SLES022C – DECEMBER 2001 – REVISED OCTOBER 2007
TYPICAL PERFORMANCE CURVES OF INTERNAL FILTER (continued)
STOP-BAND CHARACTERISTICS PASS-BAND CHARACTERISTICS
Figure 28. Figure 29.
The PCM1804 consists of a band-gap reference, a delta-sigma modulator with full-differential architecture for
L-channel and R-channel, a decimation filter with a high-pass filter, and a serial interface circuit. Figure 30
illustrates the total architecture of the PCM1804. An on-chip, high-precision reference with 10- μ F external
capacitor(s) provides all the reference voltage needed in the PCM1804, and it defines the full-scale voltage range
of both channels. Full-differential architecture provides a wide dynamic range and excellent power-supply
rejection performance. The input signal is sampled at × 128, × 64, and × 32 oversampling rates according to the
overasmpling ratio control, OSR[0:2]. The single rate, dual rate, and quad rate eliminate the external sample-hold
amplifier. Figure 31 illustrates how for each oversampling ratio the PCM1804 decimates the modulator output
down to PCM data when the modulator is running at 6.144 MHz. The delta-sigma modulation randomizes the
modulator outputs and reduces the idle tone level. The oversampled data stream from the delta-sigma modulator
is converted to a 1-f
S
, 24-bit digital signal, while removing high-frequency noise components using a decimation
filter. The dc components of the signal are removed by the HPF, and the HPF output is converted to a
time-multiplexed serial signal through the serial interface, which provides flexible serial formats and master/slave
modes. The PCM1804 also has a DSD output mode. The PCM1804 can output the signal directly from the
modulators to DSDL (pin 16) and DSDR (pin 15).
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Product Folder Link(s): PCM1804