Matched filter

A matched filter, which, each time a predetermined input clock is inputted thereto, carries out correlation operations between an analog signal and correlation filter coefficients the number of which is not more than a predetermined maximum length, comprising:

• sample-hold circuits which are placed in parallel with each other with the number being at least the same as the maximum length and to which the analog signal is inputted;
• a correlation filter coefficient register which is constituted by first registers that are installed in association with the sample-hold circuits and which allows first register values to cyclicly shift step by step for each input clock, the first register values indicating the correlation filter coefficients related to the corresponding sample-hold circuits at the current cycle of the input clock;
• operation means for carrying out correlation operations based upon the combinations of the first register values of the correlation filter coefficient register and the outputs of the corresponding sample-hold circuits;
• an output-suppressing register which is constituted by second registers that are installed in association with the sample-hold circuits and which allows second register values to cyclicly shift step by step for each input clock, the second register values indicating whether or not the output of the corresponding sample-hold circuit contributes to a correlation operation at the current cycle of the input clock;
• multiplexors which are placed in association with the sample-hold circuits and which select either the outputs of the sample-hold circuits or the operational reference electric potential so as to input them to the operation means;
• and
• multiplexor control means which, if the second register value indicates no contribution to the correlation operation, allows the corresponding multiplexor to select the operational reference electric potential.

A control method of a matched filter that has a predetermined number of sample-hold circuits of a capacitive-coupling type, the sample-hold circuits being capable of sampling and holding an inputted analog signal and performing a refreshing operation and being placed in parallel with each other, and that carries out correlation operations between correlation filter coefficients and the analog signal based upon outputs of the sample-hold circuits and the correlation filter coefficients the number of which is smaller than the predetermined number each time an input clock is applied, the control method comprising:

• a sampling step of, supposing that ordinal numbers are allocated to the sample-hold circuits cyclicly, at the time when one cycle of the input clock has elapsed from the time of sampling of the sample-hold circuit with one number before, allowing the corresponding sample-hold circuit to sample the analog signal;
• a holding step of holding the value that has been sampled at the sampling step until at least a period obtained by multiplying the input clock cycle by the number of the correlation filter coefficients has elapsed;
• and
• a refreshing step of refreshing the corresponding sample-hold circuit between the holding step and the next sampling step.