# Patent

## Title
Multiplication circuit for multiplying analog inputs by digital inputs

## Abstract

A multiplication circuit for controlling an analog input voltage by the use of a switching signal created by a digital voltage so as to either generate an analog output or to cut-off the output. A digital input signal having a plural number of bits with given weights are introduced by use of capacitive coupling, and the resulting total becomes the multiplication result.

## Background
1. Field of the Invention

The present invention relates to a multiplication circuit for multiplying an analog signal by digital signals.

2. Description of the Art

In recent years, there has been controversy over the limitations of digital computers due to the exponential increase in the amount of money invested in equipment relating to minute processing technology. Thus, analog computers are now receiving greater attention. On the other hand, conventional digital storage technology should be used and thus, both digital processing and analog processing which work together are necessary. However, conventionally, a circuit which directly operates on analog and digital data without using A/D and D/A converters has not been previously known.

The present invention is invented so as to solve the problems mentioned above. The multiplication circuit, according to the present invention, is capable of directly multiplying an anolog signal and digital signals without the need for A/D or D/A converting.

A multiplication circuit according to the present invention controls an analog input voltage by the use of a switching signal created by a digital voltage so as to either generate an analog output or to cut-off the output. A digital input signal of a plural number of bits with given weights are introduced by means of capacitive coupling, and the total becomes the multiplication result. Furthermore, the invention operates by classifying the bits of digital data, then weighing them in the group and in a group unit, and then expansion of the range of values of the capacitance is controlled.

FIG. 1 is a circuit showing an embodiment according to the present invention.

Hereinafter, an embodiment of a multiplication circuit according to the present invention is described with reference to the attached drawings.

In FIG. 1, a pultiplication circuit has switching means SW.sub.0 to SW.sub.7, wherein an anolog data V.sub.in is input. The switching means are controlled for switching by each bit b.sub.0 to b.sub.7 of the digital signal. The switching means are classified into 2 groups: the first group being G.sub.1 and the second group being G.sub.2. The first group G.sub.1 has switching means SW.sub.0 to SW.sub.3, and the second group G.sub.2 has switching means SW.sub.4 to SW.sub.7. Each group is connected by capacitive couplings CP.sub.1 and CP.sub.2, respectively.

Capacitive coupling CP.sub.1 consists of capacitances C.sub.0 to C.sub.3. Capacitive coupling CP.sub.2 consists of capacitances C.sub.4 to C.sub.7. Capacitances C.sub.0 to C.sub.3 have capacities in proportion to weights b.sub.0 to b.sub.3, respectively. Capacitances C.sub.4 to C.sub.7 have capacities in proportion to weights b.sub.4 to b.sub.7, respectively. Furthermore, CP.sub.1 and CP.sub.2 are connected to a ground potential through capacitances C.sub.11 and C.sub.13.

The outputs of CP.sub.1 and CP.sub.2 are input to inverters INV.sub.1 and INV.sub.2, respectively, and the outputs of inverter INV.sub.1 and INV.sub.2 are connected through capacitive coupling CP.sub.3. The output of CP.sub.3 is output as analog data V.sub.out through an inverter INV.sub.3, and CP.sub.3 is connected to a ground potential through capacitance C.sub.32.

The three inverters INV.sub.1 to INV.sub.3 are serially connected, and accurate outputs of each inverter is maintained. In each inverter, its output is fed back to the input through C.sub.10, C.sub.12 and C.sub.31. The capacitiies are set as follows.

If the gain of INV.sub.1 to INV.sub.3 is defined as G, the voltages impressed on C.sub.0 to C.sub.7 are defined as V.sub.0 to V.sub.7, the input voltages of INV.sub.1 and INV.sub.2 are defined as V.sub.11, and V.sub.12, respectively, the output voltages are defined as V.sub.21 and V.sub.22, respectively, and the input voltage of INV.sub.3 is defined as V.sub.31, then formulas (4), (5) can be obtained. ##EQU1##

Under certain conditions formulas (6) and (7) can be established. -V.sub.out)+C.sub.32 V.sub.31 =0                          (6)

Then formulas (8) and (9) can be defined as follows. ##EQU2##

Formula (10) is then obtained.

When SW.sub.1 is connected with V.sub.in or the ground potential corresponding to b.sub.0 to b.sub.7, and V.sub.i is equal to V.sub.in or 0, and following formulas are obtained.

wherein Cu is an unit capacity

Therefore, the final output becomes a multiplication result of an anolog signal and digital signals.

Formula (16) can then be defined as follows. ##EQU3##

When formula (17) is true, then formula (18) is obtained. ##EQU4##

A level of formula (18) is twice that of formula (16). By this type of level controlling, a moving are can be selected.

As shown by formula 12, bits b.sub.0 to b.sub.3 and b.sub.4 to b.sub.7 of digital data are in different groups and a weight is given to each of the bits. The order of 2.sup.3 is sufficiently in the range of capacticances C.sub.0 to C.sub.7, because the multiplication result of higher groups are given a weight corresponding to the group.

As mentioned above, a multiplication circuit according to the present invention controls an analog voltage by the use of a switching signal of a digital voltage so as to either generate an anolog output or to cut off the output. A digital input signal of a plural number of bits are given weights by means of capacitive coupling, and the total becomes a multiplication result. Furthermore, the invention operates by classifying the bits of digital data, then weighing them in the group and in a group unit, and then expansion of the range of values of the capacitance is controlled.

## Claims

1. A multiplication circuit for multiplying an analog signal and a digital signal having bits comprising: which said bits of said digital signal are classified, each said first capacitance having a capacitance value corresponding to a bit weight to be assigned to said bits of each said corresponding group; that is included in each of said corresponding groups, each said second capacitance having a capacitance values corresponding to a bit weight to be assigned to each said bit; and said first capacitance.

2. A multiplication circuit according to claim 1, wherein said digital data includes 8 bits.

3. A multiplication circuit according to claim 1, wherein each said group includes 4 bits.

4. A multiplication circuit according to claim 1, further comprising an amplifier having a feed back system, and wherein an output of said multiplication circuit is voltage compensated by said amplifier.