JPS5917663A - Multiplier - Google Patents

Abstract

PURPOSE:To remove switching noises from a multiplier for digital and analog values by adding an output from a DA converter in which an analog input is applied to its reference voltage terminal to the output of a DA converter of which reference voltage terminal is grounded. CONSTITUTION:An analog output proportional to the product of a digital input inputted from a data latch 36 to an input terminal 1a and the analog input of a terminal 12a is obtained from a terminal 13a of a DA converter 11a, and an analog output proportional to the product of the complement of a digital input and an analog input is obtained from a terminal 14a. Since an input terminal 12b is grounded, no output is generated from output terminals 13b, 14b of a DA converter 11b. The output of an operational amplifier 39 is inverted, the inverted signal is applied to an operational amplifier 38 and the multiplied result is obtained from a terminal 22. Switching noises in respective DA converters have reverse polarity each other at a connection point 44, so that the switching noises are offset.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multiplier that multiplies a digital value by an analog value and outputs an analog value.

<Background> As such a multiplier, a digital input is applied to the digital input terminal of a DA converter, an analog input is applied to the reference voltage terminal, and an output proportional to the product of the digital input and the analog input is output to the analog output terminal. It is possible to obtain

For example, as shown in FIG. 1, an n-bit digital input is applied to digital input terminals 11 to 1fl of a DA converter 11 using a resistance ladder circuit, and an analog input is applied to a reference voltage terminal 12 to which a reference voltage is to be applied. be done. An analog output proportional to the product of the digital input and the analog input is obtained at the analog output terminal 13 of the DA converter 11.

In the case of a negative digital input, an analog output proportional to the product of the digital input and the analog input is obtained at the complement analog output terminal 14. Analog output terminal 13 is operational amplifier 1
A feedback resistor 16 is connected between the input and output terminals of the operational amplifier 15, and a smoothing capacitor 17 is connected in parallel with the resistor 16. The terminal 14 is also connected to the inverting input terminal 1 of the operational amplifier 18, a feedback resistor 19 is connected between the input and output terminals of the operational amplifier 18, and the output terminal thereof is connected to the inverting input terminal of the operational amplifier 15 through the resistor 21. .

Each inverting input side of the operational amplifier 15.18 is grounded through a Schottky diode 23.24 to limit each positive and negative pulsed voltage and to prevent pulsed noise from being connected to the capacitor 1.
Remove with 7.

Such a multiplier can relatively easily multiply an analog quantity and a digital quantity, but it can also multiply digital values at high speed.
When switching, switching noise occurs. That is, the DA converter 11 has one end of a resistance ladder circuit 25 connected to the reference voltage terminal 12, as shown in FIG.
1 to 2n are selectively connected to analog output terminals 13.14 by changeover switches 31 to 3n. Switches 31-3n
is switched and controlled by each bit of the digital input, and the switch 31 corresponds to the least significant bit and the switch 3n corresponds to the most significant bit. The switches 31 to 3n are composed of, for example, MOS transistors.

An equivalent circuit of this one switch 31 portion is shown in FIG. When the output terminal 13.14 is connected to the ladder circuit 25 by the switch 31, the voltage source 27.26 of the voltage V+ obtained by dividing the terminal 120 voltage ■ is connected, and the terminal 1
3.14, when the switch 31 is switched, the switching noise source 31 and 32 generated by the control signal leaking through the coupling capacitance between the input and output electrodes of the switch is connected, and the capacitance is further increased due to the change in the applied voltage when the switch is switched. Load capacitances @33, 34 whose values vary are also connected to terminals 13, 14, respectively. As described above, due to the existence of the load capacity ff133.34 that changes depending on the noise source 31.32 and the digital input, a correct multiplication output cannot be obtained.

<Summary of the Invention> An object of the present invention is to provide a multiplier that uses a DA converter to multiply a digital quantity and an analog quantity without inputting noise (and obtaining a correct output).

According to this invention, first. A second DA converter is used,
A common digital input is applied to each of the digital input terminals, an analog input is applied to one reference voltage terminal, and □
The other reference voltage terminal is grounded, and these first . 2nd DA
The output of one analog output terminal of the converter and the output of the other complement output terminal are added by an adder circuit to obtain an output proportional to the product of the digital input and the analog input. If you do it like this, 1. Switching noise of the second DA converter is canceled out, and changes in load capacitance are also mutually canceled out, so that a correct multiplication output can be obtained.

<Embodiment> FIG. 4 shows an example of a multiplier according to the present invention, in which DA converters 11a and Ilb are provided, and a digital input is commonly applied from a data latch 36 to each digital input terminal 1a and lb. The digital input to the data latch 36 is taken in by the clock at the terminal 37. An analog input is applied to the reference voltage terminal 12a of one DA converter 11a, and the reference voltage terminal 1 of the other DA converter iib
2b is grounded. The analog output terminal 13a of the DA converter 11a and the complement output terminal 14b of the DA converter 11b are both connected to the inverting input terminal of the operational amplifier 38.

The complement output terminal 14a of the DA converter 11a and the analog output terminal 13b of the DA converter 11b are both connected to an operational amplifier 39.
connected to the inverting input terminal of Feedback resistors 41 and 42 are connected between each inverting input terminal and output terminal of the operational amplifiers 38 and 39, and each non-inverting input terminal is grounded. The output terminal of the operational amplifier 39 is connected to the inverting input terminal of the operational amplifier 38 through the resistor 43, and the output terminal of the operational amplifier 38 is used as the multiplication output terminal 22.

According to this configuration, the terminal 13a of the DA converter 11a has
An analog output proportional to the product of the digital input at input terminal 1a and the analog input at terminal 12a is obtained, and an analog output proportional to the product of the complement of the digital input at terminal 1a and the analog input at terminal 12a is obtained at terminal 14a. It will be done. On the other hand, since the terminal 12b of the DA converter 11b is grounded, the output from both the terminals 13b and 14b becomes zero.

Therefore, the outputs of terminals 13a and 14a are respectively supplied to operational amplifiers 38 and 39, the output of operational amplifier 39 is inverted and supplied to operational amplifier 38, and terminal 22 has a digital input as described in connection with FIG. The result of multiplication with the analog input is obtained.

Each of the DA converters 11a and 11b is configured as shown in FIG. 2, for example. Therefore, the equivalent circuit for the portion controlled by one bit of the digital input is shown in FIG. For example, terminals 13a, 1
4b, the first bit in the digital input causes the DA conversion gt
! 1.1 A signal source 27a of voltage vI is connected to the connection point 44 from the a side, and a switching noise source 31a and a load capacity fii 33a are also connected. The output of the signal source 28b on the DA converter 11b side is Ov because the reference voltage terminal 12b is grounded, and the voltage switching noise source 3
2b and the load capacitor 34b are connected to the connection point 44.

The sound of the switching noise source 31a is generated when the switch is turned on.
The noises 2b are generated when the switch is turned off, have opposite polarities, and are canceled out at the connection point 44.

Further, the capacitances of the load capacitors 133a and 34b always change inversely to each other, and since these capacitances are connected in parallel, their sum is always constant. In this way, the noise generated during switching is canceled out. Terminal 14a in Figure 4
, 13b, is similarly unaffected by switching noise and changes in load capacitance.

[Brief explanation of the drawing]

Figure 1 shows the proposed multiplier, Figure 2 shows the DA
A connection diagram showing an example of a converter, FIG. 3 is an equivalent circuit diagram for one bit of digital input of a DA converter, FIG. 4 is a connection diagram showing an example of a multiplier according to the present invention, and FIG. It is an equivalent circuit diagram of one bit of the digital input. ia, 1b: digital input terminal, 11a, llb:
DA converter, 12a, 12b: reference voltage terminal, 13a,
13b: Analog output terminal of DA converter, 14a
, 14 b: DAWm device (D'M number 7 + log output terminal, 22: Sliding output terminal, 38, 39: operational amplifier for analog addition circuit. Patent applicant: Tagada Riken Kogyo Co., Ltd.)
Written amendment to the procedure by Takashi Kusano (spontaneous) October 15, 1981 1, Indication of the case: Japanese Patent Application No. 57-1278322, Title of the invention: Multiplier 8, Person making the amendment: Relationship with the case: Patent applicant Takeda Riken Kogyo Co., Ltd. 4, Agent 4-2-21 Shinjuku, Shinjuku-ku, Tokyo
Sumo Building 5, subject of amendment Drawing 6, contents of amendment (1) Figure 2 of the drawing will be corrected to the attached drawing. le 2 figure 5

Claims (1)

[Claims] (1) The first digital input terminal receives a digital input and the reference voltage terminal receives an analog input.
A DA converter has the same configuration as this first DA converter, and the digital input is given to the digital input terminal,
and a second DA converter whose reference voltage terminal is given a ground potential, the analog output of one of the first DA converter and the second DA converter, and the complement analog output of the other, and the digital input and the analog input are added together. and an adder circuit that outputs the product of .