JPH04167812A - Pulse width conversion circuit - Google Patents

Abstract

PURPOSE:To attain pulse conversion excellent in linearity even when a period of an input signal is short by operating a differential switching circuit with the input signal at a prescribed period so as to charge/discharge a capacitor with a current from a current source, thereby generating a reference pattern signal. CONSTITUTION:A digital input signal (d) is inputted to a comparator 2 via a D/A converter 11. On the other hand, a triangle wave as a reference pattern signal from a triangle wave generating circuit 13 is inputted to the comparator 12 and when the triangle wave is lower than the level of an analog signal from the D/A converter 11, a pulse width signal at an L level is generated and when the triangle wave is higher than the level of the analog signal from the D/A converter 11, a pulse width signal at an H level is generated. In this case, an input signal (h) at a prescribed period is inputted to the bases of transistors(TRs) 16, 17 in the circuit 13 via a buffer circuit 14 and an inverter 15 and the TRs 16, 17 are switched in response to the signal (h). When the signal (h) at an H level, the TR 16 is turned on and the TR 17 is turned off and the setting current of a current source 18 flows to the TR 16 and a current equal to the setting current flows to a TR 20 to charge a capacitor 23, and when the signal (h) is at an L level, the capacitor 23 is discharged and a triangle wave is generated.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a pulse width conversion circuit.

[Conventional technology]

In recent years, with the development of digital technology, many circuits that use pulse width to perform various types of control have come into use, and the importance of pulse width conversion circuits that change the duty ratio without changing the pulse period is increasing. .

FIG. 6 shows an example of a conventional pulse width conversion circuit, and FIG. 7 shows waveforms of various parts thereof.

This pulse width conversion circuit includes resistors 1 and 2, a capacitor 3, an operational amplifier 4, a comparator 5, a reference voltage generation circuit 6, a signal input terminal 7, a ground terminal 8, and an output terminal 9.

The operation of the pulse width conversion circuit configured in this manner will be described below with reference to FIG.

First, a constant period signal applied to the signal input terminal 7 is composed of resistors 1 and 2, a capacitor 3, and an operational amplifier 4. It is integrated by an integrating circuit and becomes a triangular wave j. This triangular wave i and the reference voltage j obtained from the base voltage generation circuit 6
are compared by the comparator 5, and an output signal k having a low level appears at the output terminal 9 in the section where the triangular wave i is lower than the reference voltage j. If the duty ratio of this output signal is defined as the ratio of the time Th during which the output signal k is at a high level and the time T1 during which the output signal k is at a low level, then the duty ratio of the output signal is calculated from the reference voltage generation circuit 6. This can be changed by controlling the obtained reference voltage j. In addition, when changing the period of a constant period signal applied to the signal input terminal 7, the period of the input signal is changed and at the same time, the resistors 1 and 2, the capacitor 3, and the operational amplifier 4 are
The integration coefficient of the integration circuit configured by the above may be changed, or a plurality of integration circuits may be prepared and these may be used selectively depending on the period of the input signal.

Furthermore, Japanese Patent Laid-Open No. 2-69019 discloses a first charging circuit having a first charging time constant, and a second charging circuit having a second charging time constant smaller than the charging time constant of the first charging circuit. a switch for discharging both charging circuits in phase synchronization with an input signal of a constant period; and a switch for discharging the second charging circuit in phase synchronization with the input signal, prior to discharging operation of the switch; sample and hold circuit,
a comparison circuit that compares the holding voltage of the sample and hold circuit with the charging voltage of the first charging circuit, and changes the output level in a binary manner according to the magnitude thereof; A pulse width conversion circuit is described, characterized in that a converted signal is obtained as the output of the comparison means.

[Problem to be solved by the invention]

In the pulse width conversion circuit shown in FIG. 6 above, when the period of the input signal applied to the signal input terminal 7 is shortened, it is difficult to obtain good linearity due to problems with the operating speed of the calculation tank @ unit 4. Since it becomes impossible to obtain the triangular wave i, and furthermore, it becomes impossible to rapidly change the slope of the triangular wave i, it becomes difficult to obtain an output waveform with a narrow pulse width (with a small or large duty ratio). Moreover, since the output of the operational amplifier 4 is a triangular wave i that depends on the waveform of the constant-cycle signal applied to the signal input terminal 7, if you try to obtain a pulse with good linearity and a small duty ratio, the signal The required accuracy becomes stricter and the circuit becomes more complex. In addition, when changing the period of the input signal applied to the signal input terminal 7, the period of the input signal is changed, and at the same time, the integration of the integrating circuit constituted by the resistor 1, 2° capacitor 3 and operational amplifier 4 is performed. The circuit configuration becomes complicated because the coefficients are changed or a plurality of integrating circuits are prepared and these are selectively used depending on the period of the input signal.

Furthermore, the pulse width conversion circuit described in JP-A-2-69019 requires a switch, etc. to discharge the charge of the capacitor, so it has the disadvantage that it is difficult to reduce the period of the input signal with a constant period. .

The present invention improves the above-mentioned drawbacks and provides a pulse width conversion circuit that can perform pulse width conversion with good linearity even if the period of the input signal is short, and can respond to changes in the period of the input signal with a simple configuration. The purpose is to

[Means to solve the problem]

To achieve the above object, the invention of claim 1 provides a reference pattern signal that generates a reference pattern signal by switching a differential switching circuit using an input signal of a predetermined period and charging and discharging a capacitor with a current from a current source. The invention according to claim 2 is characterized in that it comprises a generation circuit, a digital/analog converter that converts digital data into an analog signal, and a comparator that compares the reference pattern signal and the analog signal. The pulse width conversion circuit described above includes current variable means for changing the set current of the current source.

[For production]

In the first aspect of the invention, the reference pattern signal generating circuit generates the reference pattern signal by switching the differential switching circuit in response to an input signal of a predetermined period and charging and discharging a capacitor with the current of the constant current source.
An analog converter converts the digital data into an analog signal, and a comparator compares the reference pattern signal and the analog signal.

Further, in the invention according to claim 2, the set current of the current source is changed by a current variable means.

〔Example〕

FIG. 1 shows a first embodiment of the invention.

The input signal d is digital data and is converted into an analog signal by a digital/analog (D/A) converter 11 and input to a comparator 12. On the other hand, a reference pattern signal generation circuit 13 consisting of a triangular wave generation circuit generates a triangular wave as a reference pattern signal in response to an input signal of a constant period and outputs it to the comparator 12. The comparator 12 compares the analog signal from the D/A converter 11 and the triangular wave from the triangular wave generation circuit 13, and when the triangular wave is at a lower level than the analog signal, it becomes a low level and the triangular wave is at a lower level than the analog signal. When the level is high, a pulse width signal that becomes high level is output. The duty ratio of this pulse width signal changes with the period of the input signal according to the input signal d. FIG. 2 shows the configuration of the triangular wave generation circuit 13.

For input signals with a constant period, the buffer 14 and the inverter 15
1 to the bases of transistors 16 and 17, respectively, and transistors 16 and 17 switch according to the input signals. When the input signal is at a high level, the transistor 16 is turned on and the transistor I7 is turned off, and the set current of the current source 18 flows to the transistor 16, and the transistors 19 to 2I and the resistor 2I are turned off.
2, a current equal to the set current of the current source 18 flows as a collector current of the transistor 20.

The capacitor 23 is charged by the collector currents of the transistors 1 to 20. As a result, when the set current of the current source 18 is 1 and the capacitance of the capacitor 23 is C, the voltage between the terminals of the capacitor 23 increases according to I X t/C (t: time). On the other hand, when the input signal R is inverted to a low level, transistors 1 to 16 are turned off and transistor 17 is turned on. At this time, no current flows through the current mirror circuit constituted by the transistors 19 to 21 and the resistor 22, and the collector currents of the transistors 1 to 20 become O. Since the transistor 17 is on, the set current (2) of the current source j8 flows through the transistor 17, and the electric charge in the capacitor 23 is discharged by this current (2). As a result, the voltage between the terminals of capacitor 23 decreases according to IXt/C. In this way, the capacitor 23 is charged and discharged, and the capacitor 2
A triangular wave voltage is generated between the terminals 3 and 3, and this triangular wave voltage is output to the comparator 12. The transistors 16 and 17 constitute a differential switching circuit, and can operate at high speed to reduce the error of the triangular wave.

FIG. 3 shows a triangular wave generating circuit in a second embodiment of the invention.

This second embodiment uses the triangular wave generating circuit shown in FIG. 3 as the triangular wave generating circuit 13 in the first embodiment. In FIG. 3, the same parts as in FIG. 2 are given the same reference numerals. In this triangular wave generation circuit, a bias current is passed from a current source 24° 25 to a current mirror circuit constituted by transistors 19 to 21 and a resistor 22, and the first transistors 19 to 21 operate without being turned off, resulting in higher speed. can.

FIG. 4 shows a triangular wave generating circuit in a third embodiment of the present invention.

This third embodiment uses the triangular wave generating circuit shown in FIG. 4 as the triangular wave generating circuit 13 in the second embodiment. In FIG. 4, the same parts as in FIG. 3 are given the same reference numerals. In this triangular wave generation circuit, the voltage between the terminals of the capacitor 23 is 1 - the resistor 26 and the resistor 2.
7 converts it into a current and inputs it into a current mirror circuit constituted by transistors 28 to 31 and a resistor 32, and a current equal to the collector current of transistor 26 flows through transistors 28 and 31. The collector current of the transistor 31 is converted into a voltage by the resistor 33 and output as a triangular wave voltage to the comparator 12, and the capacitor 35 is charged and discharged by the error current between the collector current of the transistor 28 and the set current of the current source 34. . The voltage between the terminals of this capacitor 35 is converted into a current by a transistor 36 and a resistor 37, and flows as a bias current to a current mirror circuit constituted by 1-transistors 19 to 21 and a resistor 22. Therefore, the charge in the capacitor 23 is discharged so that the set current of the current source 34 and the average value of the collector current of the transistor 28 become equal, the collector current of the transistor 31 is stabilized, and the voltage between the terminals of the resistor 33 is stabilized. Ru.

FIG. 5 shows a triangular wave generation circuit in a fourth embodiment of the present invention.

This fourth embodiment uses the triangular wave generating circuit shown in FIG. 5 as the triangular wave generating circuit 13 in the third embodiment. In FIG. 5, the same parts as in FIG. 4 are given the same reference numerals. In this triangular wave generating circuit, instead of the set current of the current source 18, the collector current of the transistor 38 is set from 1 to 16. Flows to +7. Transistors 39-44. Current sources 45, 46, resistors 47, buffers 48, 49, inverters 50, 5] constitute a switching circuit, and digital current setting signals a and b are input to this switching circuit. Here, current source 4
The set currents of 5.46 are set to different values. Current setting signal a.

When both b are at high level, transistors 41 and 44
is turned on, the 1-transistors 42 and 43 are turned off, and a current corresponding to the set current of the current source 45 flows through the collector of the transistor 38. Further, when the current setting signal a is at a high level and the current setting signal is at a low level, transistors 4 and 43 are turned on and transistors 42 and 44 are turned off, and the collector of the transistor 38 is connected to the current source 4.
A current flows according to the sum of the set currents of 5.46. When current setting signals a and b are both at low level, transistors 42 and 43 are turned on, and transistors 41 and 44 are turned on.
is turned off, and a current corresponding to the set current of the current source 46 flows through the collector of the 1H transistor 38. therefore,
At the same time as changing the period of the human input signal, the current setting signal a
, b, by varying the collector current of the 1-transistor 38, the current value for charging and discharging the capacitor 23 is varied.

The period of pulse width conversion can be changed, and pulse width conversion corresponding to input signals d having different conversion periods can be performed. Furthermore, a capacitor 52 and a resistor 53 are added, and the average value of the currents flowing through the transistors 30, 28, 31 quickly becomes equal to the current value of the current source 34.

In this case, the voltage between the terminals of the capacitor 33 is applied to the base of the transistor 26 via a differential amplifier consisting of transistors 511 and 55, a current source 56, a resistor 57, and a voltage source 58.
A voltage is applied between the emitters, and the capacitor 23 is charged and discharged via the resistor 27.

〔Effect of the invention〕

As described above, according to the invention of claim 1, the reference pattern signal is generated by switching the differential switching circuit with the input signal of a predetermined period and charging and discharging the capacitor with the current of the current source. Even if the cycle is short, pulse width conversion with good linearity can be performed.

According to the second aspect of the invention, the pulse width conversion circuit according to the first aspect is provided with a current variable means for changing the set current of the constant current source, so that the pulse width conversion circuit corresponding to digital data having different conversion cycles is provided. can perform the conversion,
It can respond to changes in the input signal cycle with a simple configuration.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a circuit diagram showing a triangular wave generation circuit of the same embodiment, and Figs.
The figures are circuit diagrams showing triangular wave generation circuits according to other embodiments of the present invention, Fig. 6 is a block diagram showing an example of a conventional pulse width conversion circuit, and Fig. 7 shows waveforms of various parts of the pulse width conversion circuit. FIG. ]1...D/A converter, 12...Comparator, 13...
・Triangular wave generation circuit, 16.17, 19, 20.38-4
4...1 - transistor, 18, 45.46... current source, 23... capacitor. 4111J-Miss

Claims (1)

[Claims] 1. A reference pattern signal generation circuit that generates a reference pattern signal by switching a differential switching circuit in response to an input signal of a predetermined period and charging and discharging a capacitor with a current from a current source, and a digital A pulse width conversion circuit comprising: a digital/analog converter that converts data into an analog signal; and a comparator that compares the reference pattern signal and the analog signal. 2. The pulse width conversion circuit according to claim 1, further comprising current variable means for changing the set current of said constant current source.