JPH1188130A - Waveform shaping circuit - Google Patents

Abstract

(57) [Problem] To provide a waveform shaping circuit capable of accurately adjusting rise and fall times with a simple configuration. SOLUTION: A first and a second transistor Q having different polarities and connected in series between a high potential line 2 and a low potential line 3 are provided.
3 corresponds to a pulse generation circuit in which a pulse voltage is obtained at its connection point P1 by alternately turning on Q4. When the series circuit of the second capacitor C2 and the transistor Q2 and the transistor of the series circuit of the second capacitor C3 and the transistor Q1 are turned on, the second capacitor of the series circuit is connected to the connection point P1 and the low potential line 3
It is connected in parallel with the first capacitor C1 connected therebetween. The rise and fall times can be adjusted when the capacitor C1 is independently connected to the connection point P1 and when the capacitor C1 and the second capacitor are connected in parallel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveform shaping circuit for adjusting the rise and fall of a pulse voltage.

[0002]

2. Description of the Related Art When a digital signal is transmitted, the rise time and the fall time of a pulse voltage forming the signal are usually determined by standards. For example, in the interface circuit of a personal computer, US
There is B standard (Universal Serial Bus Specification). FIG. 3 is a circuit diagram showing such a conventional waveform shaping circuit. A pulse voltage is obtained from the operational amplifier A1, a capacitor C10 connected between its output terminal and the inverting input terminal, and a constant current source S for supplying current to the capacitor C10.
2 forms a waveform shaping circuit. The output voltage V _OUT obtained at the output terminal 10 of such a waveform shaping circuit is
Since it is given by equation (1), rise and fall times can be set. V _OUT = It / C (1) where I is the current of the constant current source S2, and t is the time.

However, in such a waveform shaping circuit, only one kind of capacitor C10 is connected as a load, and the current of the constant current source S2 cannot be finely adjusted. Therefore, the rise time and the fall time can be accurately adjusted. Difficult to do. FIG. 4 is a circuit diagram of another conventional waveform shaping circuit.
A plurality of waveform shaping circuits formed in the same manner as the waveform shaping circuit of FIG. 1 are connected in parallel. A capacitor C11 having a different capacitance value from the capacitor C10 and a constant current source S4 having a different current value from the constant current source S2 are connected to the operational amplifier A2. Is configured to be selected. A plurality of waveform shaping circuits having different rise and fall times are connected in parallel, and the rise and fall times can be adjusted by selecting one of them.However, when the entire circuit is complicated and formed by an integrated circuit, There is a disadvantage that the chip size becomes wide.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a waveform shaping circuit capable of accurately adjusting rise and fall times with a simple structure.

[0005]

According to the waveform shaping circuit of the present invention, the first and second transistors having different polarities connected in series between a high potential line and a low potential line are alternately turned on to connect the connection points. A first capacitor, a second capacitor, and the first and second capacitors.
A series circuit comprising a switch element responsive to at least one of the on-operations of the transistor, the first capacitor and the series circuit are connected in parallel between the connection point and the potential line, and the switch element By doing so, the first capacitor and the second capacitor are connected in parallel.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A waveform shaping circuit according to the present invention connects a pulse voltage by alternately turning on first and second transistors of different polarities connected in series between a high potential line and a low potential line. It corresponds to a pulse generating circuit which is obtained at a point. When the switch element of the series circuit of the second capacitor and the switch element is turned on in response to the ON operation of at least one of the first and second transistors, the second capacitor of the series circuit is connected to the connection point and the low point. It is connected in parallel to a first capacitor connected between the potential lines. Thus, the time constant of the waveform shaping circuit connected to the pulse generating circuit can be changed, and the rise and fall time of the pulse voltage can be adjusted. When the number of capacitors connected in parallel increases and the capacitance value increases, both the rise time and the fall time of the pulse voltage become longer. Conversely, when the capacitance value decreases, both the rise time and the fall time become short.

[0007]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing an embodiment of a waveform shaping circuit according to the present invention. In FIG. 1, a high-potential-side power supply line 2 connected to a terminal 1 to which a power supply voltage V _CC is applied and a low-potential-side power supply line 3 grounded
A PNP transistor Q3 and an NPN transistor Q4 are connected in series. Then, a pulse voltage is obtained at the connection point P1 by alternately turning on the transistor Q3 as the first transistor and the transistor Q4 as the second transistor. The pulse voltage at the connection point P1 rises when the transistor Q3 turns on, and falls when the transistor Q4 turns on. The waveform shaping circuit of the present invention corresponds to the pulse generating circuit surrounded by such a dotted line.

[0008] Such a pulse generating circuit can be constructed using an operational amplifier. A series circuit of a capacitor C1 serving as a first capacitor, a capacitor C2 serving as a second capacitor, and an NPN transistor Q2 serving as a switch element is connected in parallel between the connection point P1 and the power supply line 3. Further, a series circuit of a capacitor C3, which is another second capacitor, and a PNP transistor Q1 serving as a switch element is connected between the power supply line 2 and the connection point P1. The capacitor C1 and the plurality of series circuits are connected in parallel between the connection point P1 and the power supply lines 2 and 3. The input terminal of the waveform shaping circuit is the connection point P1, and an output whose rise and fall times are adjusted is obtained at the output terminal 4. 5 and 6 are control terminals for turning on the transistor Q1 and the transistor Q2, respectively.

In the waveform shaping circuit configured as described above, when the transistor Q3 is turned on, the current flows through the transistor Q3.
3. The current flows through the connection point P1 and the capacitor C1. Further, by turning on the transistor Q2 in response to the on operation of the transistor Q3, the current also flows to the capacitor C2. When the transistor Q4 is turned on, a current flows through the capacitor C1, the connection point P1, and the transistor Q4. By turning on the transistor Q1 in response to the on operation of the transistor Q4, current flows from the capacitor C3 to the transistor Q4 via the connection point P1.

In the waveform shaping circuit of the present invention, when the pulse voltage at the connection point P1 rises and falls, two different types of circuits having different time constants are formed. As a result, two types of rise time and fall time can be set, and a pulse voltage in which the rise time and fall time are adjusted can be obtained at the output terminal 4. By increasing the number of series circuits, the rise time and fall time can be finely and accurately adjusted.

FIG. 2 is a circuit diagram showing another embodiment of the waveform shaping circuit of the present invention, and the same parts as those in FIG. 1 are denoted by the same reference numerals. The pulse voltage is obtained at a connection point P1 between the transistor Q3 and the transistor Q4 connected in series between the high potential line 2 and the low potential line 3. A capacitor C4 as a first capacitor between the connection point P1 and the low potential line 3,
Further, a series circuit of a capacitor C5 as a second capacitor, a switch element SW1, and a voltage source S1 is connected in parallel. The switch element SW1 is, for example, a field-effect transistor, and can flow current in both directions.

In such a waveform shaping circuit, when the transistor Q3 is turned on, the current flows through the transistor Q3 and the connection point P.
1, flows to the capacitor C4, and also flows to the capacitor C5 by turning on the switch element SW1 in response to the on operation of the transistor Q3. When the transistor Q4 is turned on, the current flows from the capacitor C4 to the node P
1. The current flows from the capacitor C5 to the connection point P1 and the transistor Q4 by turning on the switch element SW1 in response to the ON operation of the transistor Q4. In the embodiment of FIG. 2, by using a switch element in which a current flows in both directions, it is only necessary to connect a series circuit of the switch element and the second capacitor in parallel between the connection point P1 and the low potential line 3. The number of series circuits may be increased or decreased as necessary.

[0013]

As described above, the waveform shaping circuit of the present invention can form a plurality of circuits having different time constants when the input pulse voltage rises and falls. Then, a pulse voltage whose rise time and fall time are adjusted can be obtained at the output terminal. Unlike the related art, there is no need to change the current of the current source or to connect a large number of complicated circuits such as operational amplifiers in parallel, so that the circuit configuration is simplified and the adjustment can be performed finely and accurately.
When formed on an integrated circuit, there is an advantage that the area required for the circuit can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a waveform shaping circuit according to the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the waveform shaping circuit of the present invention.

FIG. 3 is a circuit diagram showing a conventional waveform shaping circuit.

FIG. 4 is another circuit diagram of a conventional waveform shaping circuit.

[Explanation of symbols]

 2 potential line 3 potential line P1 connection point S1 voltage source

Claims (3)

[Claims] 1. The method according to claim 1, wherein the first and second transistors having different polarities connected in series between the high-potential line and the low-potential line are alternately turned on so that the rise and fall times of the pulse voltage obtained at the connection point can be reduced. A first capacitor, a second capacitor, and a series circuit including a switch element responsive to an on operation of at least one of the first and second transistors; Wherein the first capacitor and the second capacitor are connected in parallel between the connection point and the potential line, and the first capacitor and the second capacitor are connected in parallel by the operation of the switch element. . 2. The method according to claim 1, wherein the first and second transistors having different polarities connected in series between the high potential line and the low potential line are alternately turned on, so that the rise and fall times of the pulse voltage obtained at the connection point can be reduced. A waveform shaping circuit for adjusting a first capacitor, a second capacitor, and a series circuit including a switch element capable of responding to the ON operation of the first and second transistors and having a bidirectional current direction. Wherein the first capacitor and the series circuit are connected in parallel between the connection point and the low potential line, and the first capacitor and the second capacitor are connected in parallel by the operation of the switch element. Waveform shaping circuit. 3. The first and second transistors having different polarities connected in series between a high potential line and a low potential line are alternately turned on, so that the rise and fall times of a pulse voltage obtained at the connection point can be reduced. A waveform shaping circuit for adjusting, comprising a first capacitor, a second capacitor, and a plurality of series circuits including a switch element having a unidirectional current direction, wherein the first capacitor has a connection point and a low potential. Connected between the lines, the switching element of the series circuit is responsive to one of the ON operations of the first and second transistors, and between the connection point and the high-potential line for each series circuit of the same responsive switching element. The second capacitor of the series circuit is connected in parallel with the first capacitor by the switch element being responsively connected between the connection point and the low potential line. A waveform shaping circuit characterized by the following.