HA17902FPK datasheet(9/11 Pages) RENESAS

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HA17902 Series

Rev.1.00 Jun 15, 2005 page 9 of 10

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 +

(V2 – V1)

–

100k

Ω

100k

Ω

100k

Ω

100k

Ω

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 (VCC/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.

–

100k

10k

51k

100k

VCC

Vout1

Vout2

VCC/2 HA17902

HA17902

R/2

50k

+VC

C 0.05

µF

Figure 4 Voltage Controlled Oscillator

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