LTC1264 Ver la hoja de datos (PDF) - Linear Technology
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LTC1264 Datasheet PDF : 16 Pages
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LTC1264
APPLICATI S I FOR ATIO
R1
IN
R2
R3
STAGE 1
R5
R6
R6
R5
STAGE 3
R3
R2
R1
R1
INV B
INV C
HPB/NB HPC/NC
BPB
BPC
LPB
LPC
SB
SC
LTC1264
AGND
V–
V+
CLK
SA
SD
LPA
LPD
BPA
BPD
HPA/NA HPD/ND
INV A
INV D
R1
R2
R3
R5
R6
fCLK R6
R5
R3
R2
Figure 11. Mode 1b Bandpass Filter
STAGE 2
STAGE 4
OUT
1264 F11
Figures 12 and 13 show the gain response graphs of the
40kHz Butterworth bandpass design described above. The
passband gain response graph (Figure 12) shows a 40kHz
gain of – 0.4dB and a tilted passband from 37kHz to 43kHz.
These errors are due to the 1% resistors used and the side-
to-side matching of the LTC1264 fCLK-to-fCENTER ratio
which typically is 0.4%. To adjust for 0dB gain at 40kHz,
reduce the value of R1 in the first stage by 5%. To adjust
for a flat passband, adjust by ±1% the value of R6 in stages
3 and 4. Adjusting R6 compensates for the side-to-side
matching errors. Please refer to Figure 5 equations defin-
ing fO and Q as a function of R6.
The sequence of 2nd order stages and the bandpass gain
HOBP of each stage will determine the gain peaks at the
filter’s intermediate outputs. A given internal output can
have several dB more gain than the final filter output. Gain
peaks occur around the corners of the passband. The gain
peaks can be reduced by increasing the R1 resistor of the
first stage and decreasing the R1 resistor of the last stage
by the same amount (multiplying the R1 resistor of the
first stage and dividing the R1 resistor of the last stage by
2 for narrowband filter, and by 5 for wideband filter is a
good rule of thumb). This adjustment may, however,
increase the filter’s passband noise.
1.0
0.5
MODE 1b
VS = ±7.5V
0 fCLK = 1MHz
fCLK/fCENTER = 25:1
–0.5
–1.0
–1.5
–2.0
–2.5
–3.0
–3.5
–4.0
30 32 34 36 38 40 42 44 46 48 50
FREQUENCY (kHz)
1264 F12
Figure 12. Passband Gain vs Frequency
40kHz Butterworth Bandpass
10
MODE 1b
0
VS = ±7.5V
–10
fCLK = 1MHz
fCLK/fCENTER = 25:1
–20
–30
–40
–50
–60
–70
–80
–90
10 18 26 34 42 50 58 66 74 82 90
FREQUENCY (kHz)
1264 F13
Figure 13. Gain vs Frequency
40kHz Butterworth Bandpass
1264fb
12
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