XR-2211
16
Rev. 3.01
Design Instructions:
The circuit of Figure 12can be optimized for any tone detection application by the choice of the 5 key circuit components:
R
0
, R
1
, C
0
, C
1
and C
D
. For a given input, the tone frequency, f
S
, these parameters are calculated as follows:
(All resistance in ’s, all frequency in Hz and all capacitance in farads, unless otherwise specified)
a)
Choose value of timing resistor R
0
to be in the range of 10K to 50K . This choice is dictated by the max./min.
current that the internal voltage reference can deliver. The recommended value is R
0
= 20K . The final value of R
0
is normally fine-tuned with the series potentiometer, R
X
.
Calculate value of C
0
from design equation (1) or from Figure 7f
S
= f
O
:
b)
C
O
1
R
0
·fs
c)
Calculate R
1
to set the bandwidth + f (See design equation 5):
R
1
R
0
·f
0
·2
f
Note:
The total detection bandwidth covers the frequency range of f
O
+ f
d)
Calculate value of C
1
for a given loop damping factor:
Normally, = 0.5 is recommended.
C
1
1250·C
0
R
1
·
2
Increasing C
1
improves the out-of-band signal rejection, but increases the PLL capture time.
e) Calculate value of the filter capacitor C
D
. To avoid chatter at the logic output, with R
D
= 470K , C
D
must be:
C
D
16
f
C in
F
Increasing C
D
slows down the logic output response time.
Design Examples:
Tone detector with a detection band of + 100Hz:
a)
Choose value of timing resistor R
0
to be in the range of 10K to 50K . This choice is dictated by the max./min.
current that the internal voltage reference can deliver. The recommended value is R
0
= 20 K . The final value of R
0
is normally fine-tuned with the series potentiometer, R
X
.
Calculate value of C
0
from design equation (1) or from Figure 6f
S
= f
O
:
b)
C
0
1
R
0
·f
S
1
20,000·1,000
50nF