PCM3793A
PCM3794A
www.ti.com
SLAS529A–JANUARY 2007–REVISED FEBRUARY 2007
Registers 101–104
B15
B14
B13
IDX5
IDX5
IDX5
IDX5
B12
IDX4
IDX4
IDX4
IDX4
B11
IDX3
IDX3
IDX3
IDX3
B10
IDX2
IDX2
IDX2
IDX2
B9
B8
B7
B6
B5
B4
B3
B2
B1
B0
Register 101
Register 102
Register 103
Register 104
0
IDX6
IDX6
IDX6
IDX6
IDX1
IDX1
IDX1
IDX1
IDX0
IDX0
IDX0
IDX0
S107
S115
S207
S215
S106
S114
S206
S214
S105
S113
S205
S213
S104
S112
S204
S212
S103
S111
S203
S211
S102
S110
S202
S210
S101
S109
S201
S209
S100
S108
S200
S208
0
0
0
IDX[6:0]: 110 0101b (65h): Register 101
IDX[6:0]: 110 0110b (66h): Register 102
IDX[6:0]: 110 0111b (67h): Register 103
IDX[6:0]: 110 1000b (68h): Register 104
S[107:100]: Lower 8 Bits of Coefficient a1 for Second-Stage Notch Filter
S[115:108]: Upper 8 Bits of Coefficient a1 for Second-Stage Notch Filter
S[207:200]: Lower 8 Bits of Coefficient a2 for Second-Stage Notch Filter
S[215:208]: Upper 8 Bits of Coefficient a2 for Second-Stage Notch Filter
Default value: 0000 0000
These bits are used to change the characteristics of the second-stage notch filter. See Figure 39 for details.
The PCM3793A/94A provides two notch filters for the digital input to the DAC or the digital output from the ADC.
The optional filter characteristics of each filter are programmable. The characteristics are given by calculating
the coefficients for three parameters, sampling frequency, center frequency, and bandwidth, as shown in
Figure 39. All coefficients must be written as 2s-complement binary data into registers 97, 98, 99, 100, 101, 102,
103, and 104.
fC
fS: Sampling Frequency [Hz]
0 dB
fC: Center Frequency [Hz]
fb
fb: Band Width [Hz]
–3 dB
2pf
æ
ç
ç
è
C ö
÷
ø
a1 = –(1 + a2) cos
(Equation 1)
(Equation 2)
÷
fS
2pf /f
æ
ç
ç
è
S ö
b
÷
1 – tan
1 + tan
÷
2
ø
a2 =
2pf /f
æ
ç
ç
è
S ö
b
÷
÷
Frequency – Hz
2
ø
M0058-01
Figure 39. Parameter Settings for Notch Filter
The coefficients are calculated using Equation 1 and Equation 2 in Figure 39. An example follows:
fS = 16 kHz, fC = 0.5 kHz, fb = 0.2 kHz
a2 = 0.924390492 → Decimal to Hex → 3B29h
a1 = –1.887413868 → Decimal to Hex → 8735h
a2: F[215:208] = 3Bh, F[207:200] = 29h
a1: F[115:108] = 87h, F[107:100] = 35h
59
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