DETAILS OF OPERATION FREQUENCY-TO-

VOLTAGE CONVERTERS

(FIGURES 5 AND 6 )

a C-R network and the negative-going edge at pin 6 causes

the input comparator to trigger the timer circuit Just as with

a V-to-F converter the average current flowing out of pin 1

In the simple circuit of

FIGURE 5 this current is filtered in

than 10 mV peak but the response will be slow with a

01 second time constant and settling of 07 second to

01% accuracy

In the precision circuit an operational amplifier provides a

buffered output and also acts as a 2-pole filter The ripple

will be less than 5 mV peak for all frequencies above 1 kHz

and the response time will be much quicker than in

Figure 5

However for input frequencies below 200 Hz this circuit will

have worse ripple than

Figure 5 The engineering of the filter

time-constants to get adequate response and small enough

ripple simply requires a study of the compromises to be

made Inherently V-to-F converter response can be fast

but F-to-V response can not

TLH5680 – 6

Use stable components with low temperature coefficients

See Typical Applications section

Use low offset voltage and low offset current op amps for A1

recommended types LF411A or LF356

FIGURE 4 Precision Voltage-to-Frequency Converter

TLH5680 – 7

c

Use stable components with low temperature coefficients

FIGURE 5 Simple Frequency-to-Voltage Converter

c

TLH5680 – 8

02 mA

Use stable components with low temperature coefficients

FIGURE 6 Precision Frequency-to-Voltage Converter

Non-Linearity Maximum

8