LM231, LM331
SNOSBI2B –JUNE 1999–REVISED MARCH 2013
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In the simple circuit of Figure 18, this current is filtered in the network RL = 100 kΩ and 1 μF. The ripple will be
less than 10 mV peak, but the response will be slow, with a 0.1 second time constant, and settling of 0.7 second
to 0.1% 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 18. However, for input frequencies below 200 Hz, this circuit will have worse ripple than Figure 18.
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.
*Use stable components with low temperature coefficients.
See APPLICATIONS INFORMATION.
**This resistor can be 5 kΩ or 10 kΩ for VS=8V to 22V, but must be 10 kΩ for VS=4.5V to 8V.
***Use low offset voltage and low offset current op-amps for A1: recommended types LF411A or LF356.
Figure 17. Precision Voltage-to-Frequency Converter,
100 kHz Full-Scale, ±0.03% Non-Linearity
*Use stable components with low temperature coefficients.
Figure 18. Simple Frequency-to-Voltage Converter,
10 kHz Full-Scale, ±0.06% Non-Linearity
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