JPS6149715B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital mixing circuit that performs mixing control such that the sum of the mixing ratios of two digital signals converted into PCM (pulse code modulation) into natural binary numbers is always 1.

This type of mixing control is shown in the following equation.

A×C+B×(1-C) (0C1)
......1 Here, A is one digital input signal, B is the other digital input signal, and C is a mixing ratio control signal. To simply realize this control, the first equation of Equation 1
Two multiplication means must be provided for the term and the second term. Digital multipliers are so complex that they require a dedicated LSi, and their unit costs are high, so it is desirable to reduce the number of digital multipliers used.

Therefore, formula 1 is expanded to the following formula, and the multiplication means is 1
There are also ways to make it.

B+(A-B)×C......2 This means that for the calculation of the second term in Equation 2, there is a subtracter and a multiplier, and if there is an adder for addition of the first term and the second term, good. However, the sign in the parentheses of the second term depends on the input signal AB, and the multiplier must be treated as a complement (signed operation).
It is undesirable to use such a limited multiplier. In particular, when the bit length may be small, a means of substituting multiplication by P-ROM is often used, but the increase of one bit corresponding to the sign bit, which is a signed operation, cannot be ignored.

The present invention solves these conventional problems and provides 1
The present invention attempts to realize a circuit that performs mixing control such that the sum of the mixing ratios of input signals is 1 using unsigned multiplication means. The present invention will be explained below.

Further decomposition of the above equation 2 results in the following.

If A-B0 then B+ | A-B | ×C
......(3-1) If A-B<0 then B-|A-B|×C
(3-2) As is clear from the above equation, it is determined in advance whether the difference between the two input signals A and B is positive or negative. Depending on the result, if the signal processing result of either equation (3-1) or equation (3-2) is output, the second term is the absolute value of the difference between the two input signals |A-B| and the mixing ratio Called C.
In either case, positive signals are multiplied together, eliminating the need for signed multiplication means.

The figure shows the configuration of an embodiment to which the present invention is applied, in which digital input signals A and B are controlled by a mixing ratio control signal C to obtain an output signal D.

In the same figure, 1 is an absolute value circuit, 2 is a multiplier, and 3 is a multiplier.
are ALUs (Arithmetic Logic Units).

In this embodiment, both digital input signals A and B are supplied to an absolute value circuit 1, which outputs a positive and negative polarity signal at the same time as a difference absolute value signal |A-B|. The absolute value signal |A-B| is guided to one input of the multiplier 2, and the mixing ratio control signal C is supplied to the other input. Multiplier 2 multiplies these two positive numbers, rounds them to an appropriate bit length, and then
The product signal |A−B|×C is led to one input of ALU3. Further, the digital input signal B is supplied to the other input of the ALU 3. For example, ALU3 is
Addition and subtraction can be switched by a switching signal such as SN74S381, and this switching is performed by the positive and negative polarity signals generated when obtaining the absolute value signal |A-B| of the difference in the above-mentioned absolute value circuit 1. . This operation is based on the magnitude relationship of the digital input signals. If A is greater than B, addition is performed as B+|A-B|×C, and if A is smaller than B, B-|A-B|×C.
It performs subtraction. The output signal D of the ALU 3 may be a mixed signal in which the input digital signals A and B are controlled by the mixing ratio control signal C so that the sum of the mixing ratios becomes 1. The absolute value circuit used here is a generally well-known one, consisting of an adder and an Exclusiue-OR circuit, or
Alternatively, there is a method similar to ALU3 in which the subtracted value and the subtracted value are reversed, both A-B and B-A are performed, and the one that yields a positive result is selected.

Furthermore, in practice, each processing block may be sandwiched between registers to provide a pipeline system for reasons of processing speed.

As explained above, according to the present invention, one multiplier that only needs to handle positive numbers is provided, and it is possible to perform mixing processing equivalent to the conventional one. Also, as mentioned above, an absolute value circuit and a circuit for switching between addition and subtraction are required, but both can be easily processed by the ALU, and the circuit configuration is simple and effective as the signed multiplier is not required.

[Brief explanation of the drawing]

The figure is a block diagram of a digital mixing circuit according to one embodiment of the present invention. 1... Absolute value circuit, 2... Multiplier, 3...
ALU.

Claims (1)

[Claims] 1. A circuit that calculates the absolute value of the difference between two digital input signals pulse code modulated into natural binary numbers and determines whether it is positive or negative, a multiplication circuit that multiplies the absolute value signal by a mixing ratio control signal, and this multiplication circuit. 1. A digital mixing circuit comprising: a circuit for switching and outputting a calculation whether to add or subtract an output signal of the circuit from one of the digital input signals, depending on the result of the positive/negative determination.