Multiplying apparatus

The present invention relates to an operational circuit device for calculation, in particular for multiplication.

In calculating a plurality of digital signals and producing an output result as an analog signal, conventionally, as shown in Fig. 5, a plurality of input digital signals are calculated by a digital operational circuit 71, and the calculated results are supplied to an analog converter 72 to obtain an analog signal.

With the above-described conventional circuit arrangement, a digital operational circuit having a large area is used, resulting in a large operational circuit device.

The present invention is defined according to claim 1.

It is an object of the present invention to provide an improved operational circuit device.

It is another object of the present invention to provide a compact and high speed operational circuit device.

It is a further object of the present invention to provide an operational circuit device which does not use a digital operational circuit.

The other objects and advantages of the present invention will become apparent from the following detailed description when read in connection with the accompanying drawings.

EP-A-0310524 discloses a digital to analogue converting apparatus utilising constant current sources and a resistor ladder. GB-A-2170069 and US-A-3504360 disclose other digital to analogue devices. None of these documents discloses apparatus capable of carrying out multiplication.

In the drawings:

Fig. 1 is a circuit diagram of an addition operational circuit device.

Fig. 2 is a table showing the relationship between input data and output voltage of the addition operational circuit device shown in Fig. 1.

Fig. 3 is a circuit diagram of a further addition operational circuit device.

Fig. 4 is a circuit diagram of a multiplication operational circuit device according to the present invention.

Fig. 5 is a circuit diagram of a conventional addition operational circuit device.

In Fig. 1, reference numeral 1 represents an operational amplifier for outputting an analogue reference voltage, reference numerals 2 to 8 represent resistors connected in a ladder form constituting a resistor ladder unit 9. The values of the resistors 2, 3, 5, and 7 are R (ohm), and the values of the resistors 4, 6, and 8 are 2R (ohm). At an interconnection point e, a voltage appears whose amplitude corresponds to the current states at interconnection points a, b, c, and d. Reference numeral 10 represents an operational amplifier for buffering an output voltage of the resistor ladder unit 9. Reference numerals 11 to 18 represent switches which are switched in accordance with inputted digital signals. If an input digital signal is "0", the switch is disconnected, and if "1", it is connected. The switches 11 and 12 are connected to the interconnection point a between the resistors 2 and 3, the switches 13 and 14 are connected to the interconnection point b between the resistors 3, 4, and 5, the switches 15 and 16 are connected to the interconnection point c between the resistors 5, 6, and 7, and the switches 17 and 18 are connected to the interconnection point d between the resistors 7 and 8. Reference numerals 19 to 26 represent constant current sources connected in series to corresponding switches 11 to 18. *A0 to *A3 and *B0 to *B3 are the inverted bits of input data A0 to A3 and B0 to B3. *A0 to *A3 are connected to the switches 11, 13, 15, and 17, and *B0 to *B3 are connected to the switches 12, 14, 16, and 18. Two input data A and B to be added together are inverted by inverters (not shown). The switch corresponding to the inverted bit *A0 to *A3 and *B0 to *B3 having a value "1" is connected to thereby flow a predetermined current from the corresponding constant current source. Such constant currents are summed up for each digit (0-th, 1st, 2nd, and 3rd) at the interconnection points a, b, c, and d and flow into the resistor ladder unit 9. At the interconnection point e of the resistor ladder unit 9, there appears a voltage V₀ proportional to the sum of weighted currents at the interconnection points. Fig. 2 shows output voltages V₀ when one of the bits *A0 to *A3 and *B0 to *B3 takes "1", and all the remaining bits take "0". An output voltage V₀ when two or more bits take "1" can be obtained using the principle of superposition. For example, if the bits *A0 and *B0 are "1", the output voltage V₀ becomes REF - RI/8 - RI/8 = REF - RI/4 (volt). This voltage is equal to the voltage obtained when the bit *A1 or *B1 higher by one digit takes "1". If all the bits *A0 to *A3 and *B0 to *B3 are "1", the output voltage V₀ becomes REF - 30RI/8 (volt). The addition results between the data A and B are obtained as an output voltage V₀ in the manner described above.

As described above, addition can be carried out by adding currents for respective digits without using a digital adder, thereby reducing the circuit dimension.

If three or more data are to be added together, current sources for respective digits and corresponding switches are connected in parallel as shown in Fig. 3.

Fig. 4 is a circuit diagram of a multiplication operational circuit device according to the present invention. Reference numeral 1 represents an operational amplifier for outputting an analog reference voltage, reference numeral 30 represents a resistor ladder unit for generating a voltage corresponding to the current states at interconnection points . Reference numeral 10 represents an operational amplifier for buffering an output voltage of the resistor ladder unit 30. Reference numerals 31 to 46 represent switches. Reference numerals 47 to 62 represent constant current sources connected in series to the corresponding switches 31 to 46. A0 to A3 and B0 to B3 are values at respective digits of input data A and B to be multiplied together. Reference numerals 63 to 78 represent NAND gates for performing a NAND operation for each term. The switches 31 to 46 are connected when an output of the corresponding NAND gates 63 to 78 takes "1". The NAND gates 63 to 78 carry out a multiplication operation for each term (A0 to A3, B0 to B3) of the input data A and B. The constant current sources 47 to 62, switches 31 to 46, interconnection points f to l carry out an addition of the multiplied results at the same term. The resistor ladder unit 30 carries out an addition operation for each digit including a carry.

Upon input of two data A and B to be multiplied together, the switch corresponding to the bit *(A0 x B0) to *(A3 x B3) having a value "1" is connected to thereby flow a predetermined current from the corresponding constant current source. Such constant currents are summed up for each term at the interconnection points f to l and flow into the resistor ladder unit 30. At the interconnection point m of the resistor ladder unit 30, there appears a voltage V₀ proportional to the sum of weighted currents at the interconnection points. Namely, the product for each term is carried out by the NAND gate, and the results are added together by the resistor ladder circuit to output the multiplication results.

As described above, a digital multiplication circuit can be realized by one stage of NAND gates, resulting in a small circuit dimension and realizing high speed calculation.

As appreciated from the foregoing description, without using a digital operational circuit, addition of currents from constant current sources are used, so that it possible to provide an operational circuit device of small dimension and of high speed.