JPH0735458Y2 - D / A conversion circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a D / A conversion circuit.

[Outline of device]

This invention is a simple D / A conversion circuit, in which the other transistor is turned off by a control signal that turns on one of the pair of switching transistors of the constant current source circuit. With the configuration, without turning off a pair of transistors at the same time,
This is a D / A conversion circuit with stable characteristics.

[Conventional technology]

A D / A conversion circuit that converts a digital signal into an analog signal is known. For example, as disclosed in Japanese Patent Laid-Open No. 59-67707, this is provided with a plurality of constant current source circuits having switching circuits, and the switching circuits are controlled by digital signals supplied to the constant current source circuits. The current output from the constant current source circuit is supplied to the output terminal via the operational amplifier, and the analog signal corresponding to the digital signal is obtained.

[Problems to be solved by the device]

FIG. 2 is an example of the conventional D / A conversion circuit described above,
The power supply terminal (1) is connected via the transistor T ₁₁ to the drains of the transistors T ₁₂ and T ₁₃ forming the switching circuit. And the gate of the transistor T ₁₂ is
Is connected to a connection point between the transistors T ₁₄ and T ₁₆ for gate control of the series-connected transistors T _12, the transistors T ₁₄ and the gate of the T ₁₆ are both input terminals of the 1-bit unit of a digital signal (2 ₁ ) Is connected to. Also transistors
The gate of T ₁₃ is connected to the connection point between the transistors T ₁₅ and T ₁₇ for the gate control of the transistor T ₁₃ which are connected in series, the gates of the transistors T ₁₅ and T ₁₇ together through an inverter I ₁ Connected to input terminal (2 ₁ ). The drain of the transistor T _{14 and} the drain of the transistor T ₁₅ are connected to each other, and the source of the transistor T _{16 and} the source of the transistor T ₁₇ are connected to each other and grounded. The source of the transistor T ₁₂ is grounded, and the source of the transistor T ₁₃ is connected to the output current terminal (4). Then, one constant current source circuit C ₁ is configured by the transistors T _{11 to} T ₁₇ and the inverter I ₁ described above, and the transistors T ₁₂ and T ₁₃ are alternately arranged according to the signal from the input terminal (2 ₁ ). on, during on of the transistor T ₁₃ turned off, the current from the constant current source circuit is supplied to the output current terminal (4).

A plurality of constant current source circuits C _{1 to} C _n configured similarly to the above-mentioned one constant current source circuit C ₁ are connected between the power supply terminal (1) and the output current terminal (4). It The constant current source circuit C ₁ -C _n is heavy moisture corresponding to each of the 2 ⁰ to 2 ^n-1 is performed, the bit signal corresponding to ^{2 0 ~2 n-1 "0} " or "1" It is supplied to each input terminal (2 ₁ ) to (2 _n ). Then, 2 ⁰ to 2 ^n-1 of the current corresponding to each are supplied to the output terminal (4) from each current source circuit C ₁ -C _N, the input terminal (2 ₁₎ digital signals from ~ (2 _n) A current having an analog value corresponding to is obtained at the output terminal (4). In this way, the digital signal is converted into an analog signal.

By the way, in the above-described constant current source circuits C _{1 to} C _n , for example, while the gates of the transistors T ₁₄ and T ₁₆ of the constant current source circuit C ₁ are directly connected to the input terminal (2 ₁ ), The gates of the transistors T ₁₅ and T ₁₇ are connected to the input terminal (2 ₁ ) via the inverter I ₁ . Therefore, the input signal from the input terminal (2 ₁ ) is applied to the transistors T ₁₅ and T ₁₇ more than when it is supplied to the gates of the transistors T ₁₄ and T _16.
The time at which the transistor T ₁₂ is supplied to the gate of the transistor T ₁ is delayed by the amount of time through the inverter I _1.
T ₁₃ turns on. Therefore, transistors T ₁₂ and T
₁₃ There will be a period when both are off.

When both the transistors T ₁₂ and T ₁₃ are turned off, no current is output from the constant current source circuit C _1, so that the drain of the transistor T _{12 and} the drain of the transistor T ₁₃ have a connection point P ₁ of The potential rises to the power supply voltage V _DD . Then, the total amount I of current flowing through the plurality of constant current source circuits changes, and the currents to the other constant current source circuits change, which deteriorates the characteristics of the entire D / A conversion circuit. was there.

[Means for Solving the Problems]

The present invention provides a switching circuit having a pair of first and second transistors T ₁₃ and T ₁₂ of one polarity connected to a power supply terminal, and third and fourth transistors of one and other polarities. It is composed of a series circuit of T ₁₅ and T ₁₇ , and the connection midpoint of this series circuit is connected to the first transistor T ₁₃ of the pair of switching transistors,
The input signal (2 ₁ ) is supplied via the inverter circuit I ₁ ,
A series of first control means for controlling ON / OFF of the first transistor T ₁₃ according to an inverted signal of the input signal, and fifth and sixth transistors T ₁₄ and T ₁₆ of one and other polarities in series. Circuit, the midpoint of connection of the series circuit is connected to the second transistor T ₁₂ of the pair of switching transistors, the input signal is supplied, and the second transistor is supplied in response to the input signal. and a second control means for controlling the T ₁₂ on and off, the second control means, the seventh transistor of one polarity in series to the fifth transistor T ₁₄ of the polarity of the one T ₁₈ The second transistor T ₁₂ is turned off until the control signal from the first control means is supplied to the seventh transistor T ₁₈ and the first transistor T ₁₃ is turned on. To prevent it from becoming Serial second transistor T
The first transistor T ₁₃ is a D / A conversion circuit which is surely turned on when ₁₂ is turned off.

[Action]

With a simple configuration, it is possible to stabilize the total amount of current I flowing through the plurality of constant current source circuits and improve the characteristics of the D / A conversion circuit.

〔Example〕

FIG. 1 is a circuit diagram of an embodiment of the present invention, and the same components as those in FIG. 2 are designated by the same reference numerals. The difference between the example of FIG. 1 and the example of FIG. 2 is that the constant current source circuit CN
_Between the transistors T ₁₄ and T ₁₆ of one, a new transistor T
₁₈ is connected, the transistors are a means for gating the T _12, the gate of transistor T ₁₈ and the transistor T ₁₂ to the connection point between the transistor T ₁₆ is connected, further gate transistor of the transistor T ₁₈ T It is connected to the midpoint of the connection between the source of ₁₅ and the gate of the transistor T ₁₃ . Then, is that connected between the constant current source circuit CN ₁ more constant current source circuit having the same configuration as that CN ₁ -CN _n is the power supply terminal (1) and the output terminal (4).

Here, now, the H-level signal is supplied from the input terminal 2 _1, and the transistor T _12, the transistor T ₁₃ turned on is turned off.

In this case, the transistor T ₁₅ is on, the transistor T ₁₈ is off, and the transistor T ₁₈ does not turn on unless the transistor T ₁₅ turns off.

Then, the signal from the input terminal 2 ₁ changes from H level to L level. At this time, if the transistor T ₁₈ is turned on, the transistor T ₁₂ is turned off, the signal from the input terminal 2 ₁ via the inverter I _1, is supplied to the gate of the transistor T _15, the transistor T ₁₅ Transistor T ₁₈ will not be turned on until T is turned off, thus transistor T ₁₂ is turned on. Then, the transistor T ₁₅ is turned off, the transistor T ₁₃ is turned on, the transistor T ₁₈ is turned on, and the transistor T ₁₂ is turned off.

In the illustrated example, the transistors T ₁₂ and T ₁₃ may be turned on at the same time, but in this case, there is no problem because the overall current amount I is not adversely affected.

Further, the P-type transistor forming the illustrated constant current source circuit may be an N-type transistor and the N-type transistor may be a P-type transistor, so that the direction in which the current I flows may be opposite to that shown in the figure.

[Effect of device]

Thus, according to this invention, the input signal is supplied through an inverter I ₁ ~I _n, a control signal from the means for gating transistor T ₁₃ to Tn _3, the transistor T ₁₂ through T
supply to the means for gate control of n ₂ , and the transistors T _{13 to} T
transistor transistor T ₁₈ to Tn ₈ which n ₃ is until turned on to prohibit the transistors T ₁₂ to Tn ₂ is turned off
It is provided in the means for gate control of T _{12 to} Tn ₂ , and the transistor T
_{12 to} Tn ₂ and T _{13 to} Tn ₃ are turned off at the same time, and the total current amount I is not changed, so the characteristics of the D / A conversion circuit are improved with a simple configuration. can do.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a diagram showing a conventional example. (1) power supply terminal, the (2 ₁₎ ~ (2 _n) is an input terminal, (4)
An output terminal, CN ₁ -CN _n constant current source circuit, I ₁ ~I _n is an inverter _{circuit, T 11 ~T 18, Tn 1} ~Tn 8 is a transistor.

Claims (1)

[Scope of utility model registration request] 1. A switching circuit having a pair of one-polarity first and second transistors connected to a power supply terminal for switching and a series circuit of one and other polar third and fourth transistors. The connection midpoint of the series circuit is connected to the first transistor of the pair of switching transistors, an input signal is supplied through the inverter circuit, and the input signal is inverted according to the inverted signal of the input signal. It comprises a first control means for controlling ON / OFF of the first transistor and a series circuit of fifth and sixth transistors of one and other polarities, and the connection midpoint of the series circuit is for the pair of switching. Connected to a second transistor of the transistors, and is supplied with the input signal, and controls on / off of the second transistor according to the input signal. A second control means, wherein the second control means is configured such that a seventh transistor having one polarity is connected in series to the fifth transistor having one polarity and the seventh transistor is connected to the first transistor. The control signal from the control means is supplied to prohibit the second transistor from being turned off until the first transistor is turned on. When the second transistor is turned off, , A D / A conversion circuit in which the first transistor is surely turned on.