JPH0226409B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> The present invention relates to a voltage/time conversion circuit that converts voltage into time that is inversely proportional to the voltage.

<Description of Prior Art> FIG. 4 shows a circuit diagram of a conventional voltage/time conversion circuit. The reference voltage V _ref is supplied to one input terminal of the comparator 17 . The current of the first voltage controlled current source 14 is controlled by the converted voltage from the input terminal 11. When a trigger signal is supplied from the trigger terminal 13, the signal from the terminal Q of the flip-flop circuit 18 changes to an H signal, and the signal from the terminal changes to an L signal. Transistor 15 is therefore turned off, and capacitor 16 is charged by the current from first voltage controlled current source 14. The non-grounded side of the capacitor 16 is connected to the other input terminal of the comparator 17, and when the charged potential becomes equal to the reference voltage, the comparator 17 sends an H signal to the flip-flop circuit 1.
8 terminal R. Therefore, the signal from the terminal Q of the flip-flop circuit 18 changes to an L signal,
The signal from the terminal changes to an H signal. This turns on the transistor 15 and discharges the charge stored in the capacitor. Here, the time t during which the signal from the terminal Q becomes an H signal is determined by t=C×V _ref /I.

In the above circuit, the potential of the capacitor when the transistor 15 is turned on and the charge stored in the capacitor 16 is discharged is determined by the collector saturation voltage of the transistor 15. The saturation voltage changes depending on the current value I from the first voltage-controlled current source 14 and the temperature, and charging of the capacitor 15 starts using this saturation voltage as a reference potential, so that the potential reaches the voltage V _ref . time t until
is affected by the current value I and temperature. Furthermore, if the capacitor 16 is repeatedly charged and discharged at high speed, the accumulated charges at the base of the transistor 15 will cause trouble, making accurate time/voltage conversion impossible.

<Purpose of the invention> The present invention provides a voltage converter that can accurately convert voltage into time that is inversely proportional to the voltage without being affected by temperature, etc.
The purpose of this invention is to provide a time conversion circuit.

<Summary of the Invention> A voltage/time conversion circuit according to the present invention includes a capacitor whose one side is grounded, a first voltage controlled current source connected to the non-grounded side of the capacitor, and one input terminal connected to the non-grounded side of the capacitor. connected to the ground side,
a comparator to which a reference voltage is supplied from the other input terminal, a first diode whose anode is connected to the non-grounded side of the capacitor, and a second diode whose cathode is connected to the cathode of the first diode and whose anode is grounded. a second voltage-controlled current source through which twice as much current as the first voltage-controlled current source flows;
a flip-flop circuit having a terminal R connected to the output terminal of the comparator; a first transistor having a collector grounded, an emitter connected to the second current source, and a base connected to the terminal Q of the flip-flop circuit; a second transistor whose collector is connected to the connection point of the first diode and the second diode, whose emitter is connected to the second current source, and whose base is connected to the terminal of the flip-flop circuit. .

<Embodiment of the Invention> FIG. 1 shows a circuit diagram of a voltage/time conversion circuit which is an embodiment of the invention. Components in the figure that are the same as those in FIG. 4 are designated by the same reference numerals. In this circuit, capacitor 16
The anode of the first diode 19 is connected to the non-grounded side of the diode 19, the cathode of the second diode 20 is connected to the cathode of the first diode 19, and the anode of the second diode 20 is grounded. These diodes 19 and 20 have the same characteristics. Further, a second voltage-controlled current source 23 through which twice as much current as the first voltage-controlled current source 14 flows is provided, and the emitters of the first transistor 21 and the second transistor 22 are connected to this second voltage-controlled current source 23. There is. The collector of the first transistor 21 is grounded, and the base is connected to the terminal Q of the flip-flop circuit 18 via the level shift circuit 34. The collector of the second transistor 22 is connected to the connection point between the first diode 19 and the second diode 20, and the base is connected to the terminal of the flip-flop circuit 18 via the level shift circuit 35. Further, a speed up circuit 24 is connected to a terminal of the flip-flop circuit 18. This is to quickly discharge the charge accumulated in the capacitor 16 when the signal from the terminal changes to an H signal.

When a trigger signal is supplied from the trigger terminal 13, the signal from the terminal Q of the flip-flop circuit 18 changes to an H signal, and the signal from the terminal changes to an L signal. Therefore, the second transistor 22 is turned off,
First voltage controlled current source 14 begins charging capacitor 16 . When the charged potential becomes equal to the reference voltage _Vref , the comparator 17 supplies an H signal to the terminal R of the flip-flop circuit 18. As a result, the signal from the terminal Q of the flip-flop circuit 18 changes to an L signal, and the signal from the terminal changes to an H signal, turning off the first transistor 21 and turning off the second transistor 2.
Turn on 2. Therefore, the charge accumulated in the capacitor 16 is discharged through the first diode 19 and the second transistor 22. When the potential of the capacitor 16 approaches 0V, a current equal to the current value I of the first voltage-controlled current source 14 flows through the first diode 19, and a current with the current value I also flows through the second diode 22. First diode 19, second diode 2
0 has the same characteristics, and changes in the characteristics of each diode due to temperature or the like cancel each other out, so the voltage on the non-grounded side of the capacitor 16 is maintained at the voltage on the anode side of the second diode, that is, 0V. Therefore, the next voltage/time conversion can be performed after the potential of the capacitor is stabilized at 0V, so accurate voltage/time conversion characteristics can be obtained.

However, if the speed-up circuit 24 is not used, the discharging current of the capacitor 16 is equal to the charging current I, so it takes the same time as charging. Therefore, a speed-up circuit 24 is added to speed up the discharge time of the capacitor 16.

FIG. 2 shows an embodiment of the speed up circuit 24. The terminal of flip-flop circuit 18 is PNP
type transistor 28, and the non-grounded side of the capacitor 16 is connected to the diode 29.
and the base of a PNP type transistor 26. The collector of the transistor 28 is connected to a power supply of -5V, for example, and the emitter is connected to the collector of the PNP type transistor 25 and the base of the NPN type transistor 27 through a resistor 32. transistor 2
The emitter of transistor 5 and the emitter of transistor 26 are connected to a power source of, for example, 15V through a resistor 31. For example, the collector of the transistor 26 is -
Connected to 5V power supply. transistor 25
A voltage obtained by dividing a voltage of, for example, 5V by a resistor 33 and a diode 30, for example, a voltage of 0.7V is supplied to the base of the circuit. The emitter of transistor 27 is grounded, and the collector is connected to diode 2.
It is connected to the cathode of 9.

Next, the operation will be explained using the timing chart shown in FIG. As shown in A, when a trigger signal is input from the trigger terminal 13, the signal D from the terminal of the flip-flop circuit 18 changes to, for example, an L signal of -1.7V, and the transistor 22
is turned off, so the first voltage controlled current source 14 starts charging the capacitor 16. Therefore capacitor 1
The voltage B on the non-grounded side of 6 increases. In addition, along with this, the voltage E on the emitter side of the transistor 28 is
For example, it decreases from −0.1V to −1.0V. Immediately after the trigger signal is input, the voltage on the non-grounded side of the capacitor 16, that is, the base voltage B of the transistor 26
is lower than the base voltage of transistor 25, so
Transistor 26 turns on, transistor 2
5 is off. Therefore, since no current flows through the resistor 32, the base voltage F of the transistor 27 is -
It becomes 1.0V. Base voltage B of transistor 26
exceeds 0.7V, transistor 25 turns on, current flows through resistor 32, and transistor 2
7's base voltage F increases to, for example, -0.1V. The base voltage B of the transistor 26 is the reference voltage.
When V _ref is reached, comparator 17 goes high as shown in C.
A signal is applied to terminal R of flip-flop circuit 18. Therefore, the signal D from the terminal is, for example -
The L signal of 1.7V changes to, for example, the H signal of -0.8V, and along with this, the voltage E on the emitter side of the transistor 28 and the base voltage F of the transistor 27 also rise, and the base voltage F of the transistor 27 increases. It becomes 0.8V. Therefore, transistor 27 is turned on, and the charge stored in capacitor 16 is discharged through diode 29 and transistor 28. When the voltage B on the non-grounded side of the capacitor 16 drops below 0.7V, the transistor 25
is turned off, and the base voltage F of the transistor 27
falls to -0.1V, stopping the discharge by transistor 27. Thereafter, the discharge continues through the first diode 19 and the second transistor 22 until it reaches 0V.

Further, the dashed line in FIG. 3B shows the voltage on the non-grounded side of the capacitor 16 when the speed-up circuit 24 is not used, and discharging takes the same time as charging.

By using the speed-up circuit 24 as described above, the charges accumulated in the capacitor 16 can be quickly discharged. Further, when the potential of the capacitor reaches, for example, 0.7V, the speed-up circuit 24 stops discharging, and the first diode 19 and second transistor 22 then reduce the voltage to 0V.
Since the transistor 27 is discharged until it reaches
The influence of charge accumulation effect can be ignored.

<Effects of the Invention> As explained above, according to the present invention, since the charge accumulated in the capacitor can be reliably discharged, a voltage/time conversion circuit that can accurately convert voltage into time can be obtained. Further, by using a speed-up circuit, this voltage/time conversion circuit can be operated at high speed.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a voltage/time conversion circuit which is an embodiment of the present invention, and FIG. 2 is a circuit diagram which shows an embodiment of a speed-up circuit used in the present invention.
FIG. 3 is a timing chart for explaining the operation of the circuit shown in FIGS. 1 and 2, and FIG. 4 is a circuit diagram of a conventional voltage/time conversion circuit. 11: Input terminal, 12: Output terminal, 13: Trigger terminal, 14: First current source, 15, 25, 2
6, 27, 28: transistor, 16: capacitor, 17: comparator, 18: flip-flop circuit, 19: first diode, 20: second diode, 21: first transistor, 22: second transistor, 23: second Current source, 24: Speed up circuit, 29, 30: Diode, 31, 32,
33: Resistor, 34, 35: Level shift circuit.

Claims (1)

[Claims] 1 A capacitor whose one side is grounded, a first voltage controlled current source connected to the non-grounded side of the capacitor, one input terminal of which is supplied with a reference voltage, and the other input terminal of which is connected to the In a circuit consisting of a comparator connected to the non-grounded side of a capacitor and a flip-flop circuit whose terminal R is connected to the output terminal of the comparator, a voltage-controlled current source; B a first diode whose anode is connected to the non-grounded side of the capacitor; C a second diode whose anode is grounded and whose cathode is connected to the cathode of the first diode; and D a collector. a first transistor that is grounded, has an emitter connected to the second current source, and a base connected to the terminal Q of the flip-flop circuit; a collector connected to the connection point of the first diode and the second diode; A voltage/time conversion circuit comprising: a second transistor having an emitter connected to the second current source and a base connected to a terminal of the flip-flop circuit. 2. The voltage converter according to claim 1, further comprising a speed-up circuit that quickly discharges the charge accumulated in the capacitor when the potential of the capacitor reaches a reference voltage.
Time conversion circuit.