Semidigital multiplication by discrete convolution using surface acoustic wave (SAW) devices

The computation of the product of two digital numbers by discrete convolution by a surface acoustic wave (SAW) convolver is described. The principal limitations of the method are discussed as well as realistic performance numbers that can be achieved by using available SAW device technology. The multiplication is done by convolving the 2-b streams that represent two digital input operands in a SAW convolver at a rate of 100 MHz. The convolver output is the product in mixed binary representation. It consists of one analog value per digit with a resolution of 0.5%. These values are digitized at a rate of 200 MHz by an 8-b flash analog-to-digital converter and added up to form the digital result. It is shown that such a device has a very high computing power that can be adapted to special applications. One extreme is the multiplication of 256-b integer numbers, corresponding to a dynamic range of 1:10⁷⁷, at a rate of 0.2 MIPS. The other extreme is the computation of matrix products where computing speeds of 12000 MIPS can be achieved for 8-b operands, as required, for example, in image filtering applications