MOSFET_GATE_DRIVER

Published:2009/7/13 4:37:00 Author:May | From:SeekIC

This ratiometric 20-kHz voltage-to-frequency converter（VFC） provides superior performance with strain gauges and other ratio-responding transducers，even with noisy, unregulated excitation voltages. Feedback isn’t used to achieve the excellent 4-Hz linearity，so there is very low frequency jitter-period measurements can be used to get several digits of resolution even when operating at a fraction of full scale. An operational synchronizing transistor starts the VFC with zero charge at the beginning of each count Cycle，eliminating the characteristic digit jumping often encountered with VFC designs. Good linearity is attained by making the comparator’s reference voltage vary with the input voltage， which precisely compensates for the finite capacitor reset Lime∶ Period＝t1＋t2 ＝t1＋（Vcc-Vref）／AVin ＝［t1AVin＋Vcc-Vref）／AVinwhere AVin＝ΔV／Δt. If Vref is made to include the amount t1AVin, then the effect of t1 is eliminated∶ Period＝[t1AVin＋VCC-(t1AVin＋Vref)]／AVinThe MPSA-18 is a remarkably high-gain transistor，even at low currents，giving good currentSource linearity down to 0 Hz. In addition，bipolar transistors work well with the low collector voltages encountered In this single-supply，10-V design . Moreover，most single-supply op amps will work in place of the LM10. But the LM10 also has a reference amplifier that could be used to construct a 10-V excitation regulator . The LM311 propagation delay gives a reset pulse width near 400 ns，which gives the transistor time to discharge the capacitor. Also，the 311’s bias current gives a small negative offset that ensures a 0-Hz output for0 V in.



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