TSC2117 Datasheet, PDF (38/192 Pages) Texas Instruments – Low-Power Audio Codec With Embedded miniDSP, Stereo Class-D Speaker Amplifier, and Smart Four-Wire Touch-Screen Controller

TSC2117
Low-Power Audio Codec With Embedded miniDSP, Stereo Class-D
Speaker Amplifier, and Smart Four-Wire Touch-Screen Controller
SLAS550A – APRIL 2009 – REVISED JUNE 2009
www.ti.com
5.5.4.4 ADC Digital Decimation Filter Characteristics
The TSC2117 offers three different types of decimation filters. The integrated digital decimation filter
removes high-frequency content and downsamples the audio data from an initial sampling rate of
AOSR × f_S to the final output sampling rate of f_S. The decimation filtering is achieved using a higher-order
CIC filter followed by linear-phase FIR filters. The decimation filter cannot be chosen by itself; it is implicitly
set through the chosen processing block.
The following subsections describe the properties of the available filters A, B, and C.
5.5.4.4.1 Decimation Filter A
This filter is intended for use at sampling rates up to 48 kHz. When configuring this filter, the oversampling
ratio of the ADC can either be 128 or 64. For highest performance, the oversampling ratio must be set
to 128.
Filter A can also be used for 96 kHz at an AOSR of 64.
Table 5-20. ADC Decimation Filter A, Specification
Parameter
AOSR = 128
Filter gain pass band
Filter gain stop band
Filter group delay
Pass-band ripple, 8 ksps
Pass-band ripple, 44.1 ksps
Pass-band ripple, 48 ksps
AOSR = 64
Filter gain pass band
Filter gain stop band
Filter group delay
Pass-band ripple, 8 ksps
Pass-band ripple, 44.1 ksps
Pass-band ripple, 48 ksps
Pass-band ripple, 96 ksps
Condition
0…0.39 f_S
0.55…64 f_S
0…0.39 f_S
0…0.39 f_S
0…0.39 f_S
0…0.39 f_S
0.55…32 f_S
0…0.39 f_S
0…0.39 f_S
0…0.39 f_S
0…20 kHz
Value (Typical)
0.062
–73
17/f_S
0.062
0.05
0.05
0.062
–73
17/f_S
0.062
0.05
0.05
0.1
Unit
dB
dB
s
dB
dB
dB
dB
dB
s
dB
dB
dB
dB
ADC Channel Response for Decimation Filter A
(Red line corresponds to -73 dB)
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Frequency Normalized w.r.t. F_S
Figure 5-13. ADC Decimation Filter A, Frequency Response
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