CS8190

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7

Figure 7. Partial Schematic of Input and Charge Pump

R3

2.0 V

R4

CP+

Q1

Q2

Q3

0.25 V

2.0 V

CP−

C4

F to V

+

−

+

−

+

−

0

T

0

0

Ripple voltage on the F/V output causes pointer or needle

flutter especially at low input frequencies.

The response time of the F/V is determined by the time

will reduce the ripple on the F/V output but will also increase

the response time. An increase in response time causes a

very slow meter movement and may be unacceptable for

many applications.

The CS8190 has an undervoltage detect circuit that disables

With no input signal the F/V output voltage decreases and the

needle moves towards zero. A second undervoltage detect

circuit at 6.0 V(typical) causes the function generator to

generate a differential SIN drive voltage of zero volts and the

differential COS drive voltage to go as high as possible. This

combination of voltages (Figure 2) across the meter coil

moves the needle to the 0

° position. Connecting a large

capacitor(> 2000

increases the time between these undervoltage points since

the capacitor discharges slowly and ensures that the needle

moves towards 0

° as opposed to 360°. The exact value of the

capacitor depends on the response time of the system,the

maximum meter deflection and the current consumption of

the circuit. It should be selected by breadboarding the design

in the lab.