AN795

DS00795A-page 1

© 2002 Microchip Technology, Inc.

Voltage-to-Frequency/Frequency-to-Voltage Converter

FIGURE 1: Ratiometric measurement (analog division).

Author:

Michael O. Paiva,

Microchip Technology, Inc.

RATIOMETRIC MEASUREMENT (ANALOG DIVISION)

One of the most difficult circuits to build is one which will divide one analog signal by another. Two voltage-to-frequency (V/F) converters

can do such division with ease. The numerator is counted directly as a signal, while the denominator forms the time base.

Counter

Latch

Output = N

Reset

TC9400

V/F

N

One

Shot

TC9400

V/F

Latch

÷

One

Shot

TC9400

F/V

Speed

Sensor

(Optical or Magnetic)

Analog Display

DVM Display

RPM

RPM

RPM/SPEED INDICATOR

Flow rates and revolutions per second are nothing more than frequency signals, since they measure the number of events per time

period. Optical and magnetic sensors will convert these flows and revolutions into a digital signal which, in turn, can be converted to a

proportional voltage by the use of a frequency-to-voltage (F/V) converter. A simple voltmeter will then give a visual indication of the

speed.

FIGURE 2: RPM/speed indicator.