LA8608V Datasheet, PDF (9/14 Pages) Sanyo Semicon Device – 1.8 V Low-Voltage Narrowband FM-IF System

LA8608V
2. About the built-in operational amplifiers
The LA8608V has three independent operational amplifiers on chip that can be used as needed. If they are not to be used, short
the I/O pins.
Sample application 1: Noise amplifier
Using the three operational amplifiers, it is possible to form a secondary biquad bandpass filter. (For details on the filter
response characteristics, refer to the data provided later.)
Fig. 5
The calculation of the transfer function for the above diagram is as shown below.
ω₀² =
R₅
C₁C₂R₃R₄R₆
ω₀
Q
=
1
C₁R₂
H
=
R₂R₅
R₁R₄
In normal use, R₃ = R₄ = R₅ = R₆ = R_f, and C₁ = C₂ = C_f:
Therefore,
ω₀
=
1
C_fR_f
f_O
=
1
2πC_fR_f
Q = C_fR₂ x ω₀
= ^R2
R_f
H = ^R2Rf
R₁R_f
= ^R2
R₁
fo = center frequency, H = pass band gain, Q = selectivity
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