Texas Instruments PCM4201EVM, User Manual

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3.4 Sampling Mode Selection
3.5 Digital High-Pass Filter
F
3dB
f
S
48, 000
, where f
S
output sampling rate
Hardware Description and Configuration
Table 2. System Clock Source Selection
OSC2 OSC1 SYSTEM CLOCK SOURCE
LO HI X1, 22.5792MHz
HI LO X2, 24.576MHz
LO LO External Clock from connector J3 or J4
The PCM4201 supports three sampling modes, allowing the user to select the best power/performance
combination for a given application.
The Normal Speed Low Power mode provides the lowest overall power dissipation while supporting
sampling rates up to 54kHz. The modulator oversampling rate is 64f
S
for this mode.
The Normal Speed High Performance mode provides the best dynamic performance at the expense of
increased power dissipation. Sampling rates up to 54kHz are supported. The modulator oversampling rate
is 128f
S
for this mode, improving the overall dynamic range and THD+N when compared to the Low
Power mode.
The Double Speed mode supports sampling frequencies up to 108kHz with power dissipation just slightly
higher than the Normal Speed High Performance mode. The modulator oversampling rate is 64f
S
for this
mode.
The sampling mode is selected using the RATE VDD and RATE GND elements of switch SW1. Table 3
shows the settings required for each sampling mode.
Table 3. Sampling Mode Selection
RATE VDD RATE GND SAMPLING MODE
OFF ON Double Speed
ON OFF Normal Speed Low Power
OFF OFF Normal Speed High Performance
The PCM201 includes a digital high-pass filter, which is utilized to remove the DC component from the
digitized signal. The high-pass filter is located at the output of the digital decimation filter in the overall A/D
signal chain. The –3dB corner frequency of the high-pass filter is set by the following relationship:
The digital high-pass filter may be enabled or disabled using the HPFD element of switch SW1. Table 4
summarizes the HPFD switch settings. There may be a small increase distortion for low frequency inputs
(less than 100Hz) when the high-pass filter is enabled.
Table 4. Digital High-Pass Filter Configuration
HPFD HIGH-PASS FILTER FUNCTION
LO Enabled
HI Disabled
PCM4201EVM User's Guide SBAU108A – January 2005 – Revised February 2005 7