JPH0514203A - Digital/analog conversion circuit - Google Patents

Abstract

PURPOSE:To use this device for an outside load which necessitates a high speed response by providing an output switching means, and fetching the output of a digital/analog(DA) converter through a buffer amplifier or directly. CONSTITUTION:When switches 5 and 7 are turned into ON states, and a switch 6 is turned into an OFF state by a switching control signal from a control terminal 8, the output signal of a DA converter 2 is outputted through an operational amplifier 3 to an outside output terminal 4. At that time, the influence of the outside load is eased by the operational amplifier 3, a high precision is held, and this device can be used for a large power load. On the other hand, when the switches 5 and 7 are turned into OFF states, and the switch 6 is turned into ON state by the switching control signal from the control terminal 8, the output signal of the DA converter 2 is outputted directly to the outside output terminal 4. At that time, the output signal of the DA converter 2 is not outputted through the operational amplifier 3, so that the high speed response can be attained. Thus, this device can be used not only for the large power load, but also for the load which necessitates the high speed response.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital-analog converter circuit, and more particularly to a digital-analog converter circuit that can be incorporated in a semiconductor integrated circuit.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing a conventional digital-analog conversion circuit incorporating a buffer operational amplifier in a semiconductor integrated circuit. In FIG. 3, 1 is an external input terminal to which a digital signal is applied from the outside, 2 is a digital-analog converter (hereinafter abbreviated as DA converter) for converting the digital signal from the external input terminal 1 into an analog signal, 3 Is a voltage follower operational amplifier as a buffer amplifier for buffering the analog output of the DA converter 2, and 4 is an external output terminal connected to the operational amplifier 3.

Next, the operation will be described. When a digital signal is input to the DA converter 2 from the external input terminal 1,
Here, it is converted into an analog signal and output. This output signal is output to the external output terminal 4 through the operational amplifier 3. An external load is connected to the external output terminal 4, and when the load current is large, the operational amplifier 3 can operate while keeping the output voltage stable.

[0004]

Since the conventional digital-analog conversion circuit is constructed as described above, when it is output through the buffer amplifier, it is affected by an external load (for example, output voltage fluctuation due to a large load current). However, there is a problem in that the so-called settling time becomes long and it cannot be used for an external load that requires high-speed response.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain a digital-analog conversion circuit that can be used for an external load that requires a high-speed response.

[0006]

A digital-analog converter circuit according to the present invention comprises a digital-analog converter for converting an input signal from a digital signal into an analog signal, and a switching means for switching the output of the digital-analog converter. And a buffer amplifier to which the output of the digital-analog converter is selectively supplied by the switching means, and the output of the digital-analog converter is taken out through the buffer amplifier or directly. ..

[0007]

In the present invention, the output of the DA converter is taken out through the buffer amplifier or directly. As a result, one digital-analog conversion circuit can handle both the case where the external load to be connected requires a large load current and the case where a fast settling time is required.

[0008]

EXAMPLES Example 1. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. The parts corresponding to those in FIG. 3 are designated by the same reference numerals and the description thereof will be omitted. In FIG. 1, 5 is a switch connected between the output terminal of the DA converter 2 and the non-inverting input terminal of the operational amplifier 3, and 6 is connected between the output terminal of the DA converter 2 and the external output terminal 4. Switch 7 is a switch connected between the output terminal of the operational amplifier 3 and the external output terminal 4, and 8 is a control terminal to which a switching control signal for turning on / off the switches 5, 6 and 7 is supplied from the outside. .. Here, the switches 5 and 7 are interlocked with each other and are controlled to be in an off state if the switch 6 is in an on state, and conversely to be in an on state if the switch 6 is in an off state.

Next, the operation will be described. First, when importance is attached to accuracy so that the output obtained at the external output terminal 4 is not affected by an external load, the switches 5 and 7 are turned on and the switch 6 is turned off by a control signal from the control terminal 8. Then, the output signal of the DA converter 2 is output to the external output terminal 4 through the operational amplifier 3. in this case,
The operational amplifier 3 as a buffer amplifier mitigates the influence of an external load, maintains high accuracy, and can be used for a large power load. On the other hand, when high speed is important, the switches 5 and 7 are turned off and the switch 6 is turned on by the control signal from the control terminal 8. Then, the output signal of the DA converter 2 is directly output to the external output terminal 4. In this case, the delay time of the output signal obtained at the external output terminal 4 is about several tens of ns, which is about 1/1000 of the delay time of several hundred ms when passing through the operational amplifier 3, and high-speed response is possible. ..

Embodiment 2. FIG. 2 is a block diagram showing another embodiment of the present invention. 2 is different from the first embodiment in FIG. 1 in that the switch 7 is removed, the output terminal of the operational amplifier 3 is directly connected to the external output terminal 4, and the other end of the switch 6 is connected to another external output terminal 9. It was done.

Next, the operation will be described. First, when importance is attached to accuracy so as not to receive an external load, the switch 5 is turned on by the control signal from the control terminal 8 and the switch 6 is turned on.
To turn off. Then, the output signal of the DA converter 2 is output to the external output terminal 4 through the operational amplifier 3. On the other hand, when high speed is important, the switch 5 is turned off and the switch 6 is turned on by the control signal from the control terminal 8. Then, the output signal of the DA converter 2 is directly output to the external output terminal 9. Also in this case, the same effect as that of the above-described embodiment can be obtained.

In each of the above embodiments, the case where the voltage follower operational amplifier is used as the buffer amplifier has been described, but other types of amplifiers may be used.

Further, in the semiconductor integrated circuit, a multi-channel digital-analog switching circuit may be configured to include a plurality of the circuit configurations of the above-described embodiments, and it goes without saying that the same effect can be obtained in this case as well.

[0014]

As described above, according to the present invention, a digital-analog converter for converting an input signal from a digital signal into an analog signal, a switching means for switching the output of the digital-analog converter, and the digital signal described above. -A buffer amplifier to which the output of the analog converter is selectively supplied by the switching means is provided, and the output of the digital-analog converter is taken out through the buffer amplifier or directly, so that it is used for a large power load. Not only can it be used, but it can also be used for loads that require high-speed response.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a digital-analog conversion circuit according to the present invention.

FIG. 2 is a configuration diagram showing another embodiment of the digital-analog conversion circuit according to the present invention.

FIG. 3 is a configuration diagram showing a conventional digital-analog conversion circuit.

[Explanation of symbols]

 2 Digital-analog converter 3 Voltage follower operational amplifier 5 switch 6 switch 7 switch

Claims (1)

Claim: What is claimed is: 1. A digital-analog converter for converting an input signal from a digital signal into an analog signal, a switching means for switching the output of the digital-analog converter, and a digital-analog converter. A buffer amplifier whose output is selectively supplied by the switching means, and the output of the digital-analog converter is taken out through the buffer amplifier or directly.