JPS635620A - Digital/analog converter built in semiconductor integrated circuit - Google Patents

Abstract

PURPOSE:To easily form a periodical analog signal required for a semiconductor integrated circuit and having the function of a conventional D/A converter by switching the setting value of D/A convertion to either an output from a latch or an output from a timer. CONSTITUTION:Resistors 1c, 1f and resist 1g-1j constitute a D/A conversion section using the output of a 1st-4th latch circuits 10-1r as a setting value and applying resistance division to a voltage from a reference voltage input terminal 1b. Selection gates 1w-1v select a periodic output signal from 1st-4th timers 1s-1v as the control signal of selection gates 1k-1n. In selecting the output signal, a power supply Vss at the right end potential of the resistors 1g-1j and a potential inputted from a reference voltage input terminal 1b are switched periodically and an output from an analog output terminal 1a acts like a periodical analog signal such as a sinusoidal wave and a sawtooth wave.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital/analog converter (hereinafter referred to as a D/A converter) built into a semiconductor integrated circuit.

[Conventional technology]

An example of a D/A converter built into a conventional semiconductor integrated circuit is shown in FIG. 2 and will be described.

In the figure, 2a is an analog signal output terminal, 2b is a reference voltage input terminal, 2c, 2d...2j is a resistor, and 2k.

2t...--2n is a selection gate, 2o#2p.
-・-・2r is the first.

Second . . . Fourth latch circuit.

The potential at the right end of the resistors 2g to 2j can be selected from either the stain source VaS or the potential input from the reference voltage input terminal 2b to the selection game 2 to 2n, respectively. ) 2] (~2n control is the first
- This is carried out based on the values held in the fourth latch circuits 20-2r.

Next, the operation of the circuit shown in FIG. 2 will be explained.

First, the first to fourth latch circuits 20 to 2r hold the D/A conversion values from the data bus, and in response to the held data, the selection gates 2 to 2n are controlled, and the resistors 2g to 2j The right end potential is determined to be either the power supply VBI or the potential input from the reference voltage input terminal 2b.

Next, based on this determined potential, a plurality of potentials are divided by the resistors 2c to 2'' and outputted from the analog output terminal 2a.

[Problem that the invention seeks to solve]

The D/A converter built into the conventional semiconductor integrated circuit described above controls the analog output signal directly from the latch, so it is not possible to obtain periodic analog signals such as sine waves and sawtooth waves. The problem was that it was difficult to

The present invention has been made to solve these problems, and therefore, it is possible to maintain the functions of the conventional D/A converter and to easily realize periodic analog output. The aim is to obtain a converter.

[Means for solving problems]

The D/A converter built into the semiconductor integrated circuit according to the present invention includes a latch circuit that holds the D/A converted value from the data bus, and a resistance division of the voltage from the reference voltage input terminal using the output of this latch circuit as a set value. and a timer unit that counts clock input as a time count setting box from the data bus. The output from the timer section or the output from the timer section can be switched.

[For production]

In this invention, by switching and selecting the D/A conversion image constant between the output from the latch circuit and the output from the timer section, all functions of the conventional D/A converter can be maintained and periodic analog You can get the output.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 shows a built-in D/A in a semiconductor integrated circuit according to the present invention.
FIG. 2 is a block diagram showing an example of a converter.

In the figure, 1a is an analog signal output terminal, 1b is a reference voltage input terminal, and 1c, 1d...-1j are resistors.

1](, 1t...--1n and IW+IX・
......1z is each selection gate, 10#1p
. . . 1r is the first . The second latch circuit, 1s*1t...1v, constitutes a timer section that counts the clock input using the time count value from the data bus as the set value. These are the first to fourth timers.

The resistors 1c to 1f and the resistors 1g to 1j constitute a D/A converter 'is' which divides the voltage from the reference voltage input terminal 1b by using the outputs of the first to fourth latch circuits 10 to 1r as set values. are doing. In addition, the potentials at the right ends of these resistors 1g to 1j are applied to the selection gates 1 to 1n, respectively, to the stain source V88.
It is possible to select either the potential input from the reference voltage input terminal 1b or the potential input from the reference voltage input terminal 1b.
The outputs from the first to fourth latch circuits 10 to 1r or the first to fourth
Outputs from timers 18-1v can be selected.

Next, the operation of the embodiment shown in FIG. 1 will be explained.

First, select gates 1w to 1zK and select gates 1 to 1.
Periodic output signals from the first to fourth timers 13 to 1v are selected as the control signal of n. Next, by selecting this output signal 1, it is possible to periodically switch the potential input from the power supply V8g at the right end potential of the resistors 1g to 1j and the reference voltage input terminal 1b, and from the analog output terminal 1 & The output of acts as a periodic analog signal, such as a sine wave or a sawtooth wave.

〔Effect of the invention〕

As explained above, according to the present invention, the setting value of D/A conversion can be switched to either the output from the latch or the output from the timer, so it is different from the conventional D/A conversion.
Since it has the function of an A converter and can easily generate periodic analog signals necessary for semiconductor integrated circuits, it has an extremely large practical effect.

[Brief explanation of drawings]

FIG. 1 shows a built-in D/A in a semiconductor integrated circuit according to the present invention.
FIG. 2 is a block diagram showing an example of a D/A converter built into a conventional semiconductor integrated circuit. 1aφ...Analog signal output terminal, 1b...Reference voltage input terminal, 1c~1゛...Resistor, 1~'' 1n...Selection gate, 10~1r...Latch circuit , 1s~1v...timer, 1w~1z...
selection gate. Agent Masuo Oiwa Figure 1

Claims (1)

[Claims] A latch circuit that holds the digital/analog conversion value from the data bus, a digital/analog converter that divides the voltage from the reference voltage input terminal with resistance using the output of the latch circuit as a set value, and a time count from the data bus. A semiconductor integrated circuit comprising a timer section that counts clock inputs using a value as a set value, the semiconductor integrated circuit being configured to be able to switch between an output from the latch circuit and an output from the timer section as a set value for the digital/analog conversion section. A digital/analog converter built into a semiconductor integrated circuit characterized by: