NJM2760

– 5 –

s

s

s

s APPLICATION NOTE

1. Center Frequency Setting for Band Pass Filters

Band pass filters equivalent circuits as follows.

Center Frequency (fo) can be formulated as follows.

2. Output Gain Setting for RECout.

Output Voltage of RECout is adjustable by external resistor: R2

Voltage Gain (Gv) is defined as follows.

Ra

Rb

C

BPF1 (8kHz)

10 kΩ*

)

169 kΩ*

)

470pF

BPF2 (1.2kHz)

6.8 kΩ

113 kΩ*

)

4.7nF

BPF3 (300Hz)

5.6 kΩ

96.5 kΩ*

)

22nF

BPF4 (80Hz)

10 kΩ

169 kΩ*

)

47nF

Ra

to Detector

Rb

C

C

Internal Circuit

External Circuit

from Input Buffer

Ra

to Detector

Rb

C

C

Internal Circuit

from Input Buffer

External Circuit

Fig.1-a. BPF1's Equivalent Circuit

Fig.1-b. BPF2-4 's Equivalent Circuit

Table 1. Center frequency setting example

b

0

CR

π

2

Q

2

f

=

[Hz],

Q=2

]

Ω

k

[

100

]

Ω

k

[

R

G

]

Vpeak

[

Vin

]

Vdc

[

Vout

2

=