NJM4151(2003) 查看數據表（PDF） - Japan Radio Corporation

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NJM4151
(Rev.:2003)

V-F / F-V CONVERTOR

Japan Radio Corporation  

NJM4151

The one-shot is made from a voltage comparator and an R-S latch, Transistors Q12-Q15 and Q18-Q20 form the

comparator, while Q8-Q11 and Q16-Q17 make up the R-S latch. One latch output, open-collector reset transistor Q16, is

connected to a comparator input and to the terminal, pin 5. Timing resistor RO is tied externally from pin 5 to V+ and timing

capacitor CO is tied from pin 5 to ground. The other comparator input is tied to a voltage divider R3-R5 which sets the

comparator threshold voltage at 0.667V+. One-shot operation is initiated when the collector of Q7 goes low and sets the

latch. This causes Q16 to turn off, releasing the voltage at pin 5 to charge exponentially towards V+ through RO. As soon

as this voltage reaches 0.667 V+, comparator output Q20 will go high causing Q10 to reset the latch. When the latch is

reset, Q16 will discharge CO to ground. The one-shot has now completed its function of creating a pulse of period T=1.1

ROCO at the latch output, Q21. This pulse is buffered through Q23 to drive the open-collector logic circuit transistor Q32.

During the one-shot period the logic output will be in the low state. The one-shot output is also used to switch the

reference voltage by Q22 and Q24. The low T. C. reference voltage is derived from the combination of a 5.5V zener

diode with resistor and diode level shift networks. A stable 1.89 volts is developed at pin 2, the emitter of Q33.

Connecting the external current-setting resistor RS = 14.0Ω from pin 2 to ground gives 135µA from the collectors of Q33

and Q34. This current is reflected in the precision current mirror Q35-Q37 and produces the output current IO at pin 1.

When the R-S latch is reset, Q22 and Q24 will hold the reference voltage off, pin 2 will be at 0V, and the current will be off.

During the one-shot period T, the latch will be set, the voltage of pin 2 will go to 1.89V, and the output current will be

switched on.

■ TYPICAL APPLICATION

1. Single supply Voltage-to-Frequency Converter

Figure 2 shows the simplest type of VFC that can be made with the NJM4151. Input voltage range is from 0 to +10V,

and output frequency is from 0 to 10kHz. Full scale frequency can be tuned by adjusting Rs, the output current set resistor.

This circuit has the advantage of being simple and low in cost, but it suffers from inaccuracy due to a number of error

sources. Linearity error is typically 1%. A frequency offset will also be introduced by the input comparator offset voltage.

Also, response time for this circuit is limited by the passive integration network RBCB. For the component values shown in

Figure 2, response time for a step change input from 0 to +10V will be 135msec. For applications which require fast

response time and high accuracy, use the circuits of Figure 3 and 4.

Figure 2. Single Supply Voltage-to-Frequency Converter

2. Precision VFC with Single Supply Voltage

For applications which require a VFC which will operate from a single positive supply with positive input voltage, the

circuit of Figure 3 will give greatly improved linearity, frequency offset, and response time. Here, an active integrator using

one section of the NJM3403A quad ground-sensing op-amp has replaced the RB-CB network in Figure 2. Linearity error

for this circuit is due only to the NJM4151 current source output conductance. Frequency offset is due only to the op-amp

input offset and can be nulled to zero by adjusting RB. This technique uses the op-amp bias current to develop the null

voltage, so an op-amp with stable bias current, like the NJM3403A, is required.

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Ver.2003-12-09

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