HA17902 Datasheet, PDF (12/14 Pages) Hitachi Semiconductor – Quad Operational Amplifier

HA17902 Series
3. High Input Impedance DC Differential Amplifier
The circuit shown in figure 3 is a high input impedance DC differential amplifier. This circuit’s
common-mode rejection ratio (CMR) depends on the matching between the R₁/R₂ and R₄/R₃ resistance
ratios. This amplifier’s output is given by the following formula.
Vout = 1 + ^R4
R₃
(V₂ – V₁)
R₂
R₄
R₁
100kΩ
100kΩ
–
100kΩ
R₃
–
V₁
+
100kΩ
+
V₂
Vout
Figure 3 High Input Impedance DC Differential Amplifier
4. Voltage Controlled Oscillator
Figure 4 shows an oscillator circuit in which the amplifier A₁ is an integrator, the amplifier A₂ is a
comparator, and transistor Q₁ operates as a switch that controls the oscillator frequency. If the output
Vout1 is at the low level, this will cut off transistor Q1 and cause the A₁ inverting input to go to a higher
potential than the noninverting input. Therefore, A₁ will integrate this negative input state and its output
level will decrease. When the A₁ integrator output becomes lower than the A₂ comparator noninverting
input level (V_CC/2) the comparator output goes high. This turns on transistor Q₁ causing the integrator to
integrate a positive input state and for its output to increase. This operation generates a square wave on
Vout1 and a triangular wave on Vout2.
+V_C
R
100k
51k
R/2
50k
C 0.05µF
100k
V_CC
– A₁
V_CC
HA17902
– A₂
+
V_CC/2
HA17902
+
51k
Q₁
10k
Vout1
Vout2
Figure 4 Voltage Controlled Oscillator
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