Abstract: A level detector includes a comparing circuit and an integrating circuit. The comparing circuit generates pulses each having its width corresponding to the length of a time period during which the strength of an input signal is higher than a reference value. Alternatively, the comparing circuit may generate pulses each having its width corresponding to the length of a time period during which the strength of the input signal is lower than the reference value. The comparing circuit successively outputs the pulses. The integrating circuit outputs a signal having its strength corresponding to an integration value obtained by temporally integrating the signal from the comparing circuit.

Abstract: A wireless receiving circuit includes a mixer, a buffer, an active low-pass filter, and a second order passive low-pass filter which are connected between a signal input terminal and a signal output terminal. The second order passive low-pass filter is for removing an interfering wave that cannot be removed by the active low-pass filter. In the wireless receiving circuit, a first capacitor and a second capacitor are provided. The first capacitor has one terminal connected to an input terminal of the buffer and the other terminal grounded. The second capacitor has one terminal connected to an output terminal of the buffer and the other terminal grounded. These two kinds of capacitors function as the second order passive low-pass filter by being combined with input and output impedance of elements provided on the upstream side and downstream side of the capacitors.

Abstract: A wireless receiving circuit includes a mixer, a buffer, an active low-pass filter, and a second order passive low-pass filter which are connected between a signal input terminal and a signal output terminal. The second order passive low-pass filter is for removing an interfering wave that cannot be removed by the active low-pass filter. In the wireless receiving circuit, a first capacitor and a second capacitor are provided. The first capacitor has one terminal connected to an input terminal of the buffer and the other terminal grounded. The second capacitor has one terminal connected to an output terminal of the buffer and the other terminal grounded. These two kinds of capacitors function as the second order passive low-pass filter by being combined with input and output impedance of elements provided on the upstream side and downstream side of the capacitors.

Abstract: A switched capacitor filter having an anti-aliasing function includes integration circuits of multiple-stages, each of which is provided with an amplifier and a switched capacitor. At least an integration circuit of the first stage has a resistor. In the filter, bipolar transistors are used for the input stage of an amplifier in at least one of the integration circuits having a resistor. On the account of this, 1/f noise is reduced.

Abstract: A matched filter for inversely spreading a received signal using spreading signals in a spread spectrum communications receiver includes: a plurality of correlators for determining cross-correlation functions of a received signal which has been sampled at a certain timing and spreading signals having a certain section length; a delay circuit for successively transferring the spreading signals having a certain section length with respect to the plurality of correlating means by delaying timings of the transfer by a period equal to the section length of the spreading signals; and a multiplexer for successively selecting one of the cross-correlation functions outputted from the plurality of correlating means, by a period equal to a sampling interval of the received signal. As a result, a matched filter with a small circuit size and low power consumption is realized.

Abstract: There is provided an encoding and decoding apparatus which can provide a high quality of reproduction of sound. There are provided an encoding section and a decoding section. A block length determining section of the encoding section time-sharingly divides an input signal into blocks having a block length corresponding to the degree of change of the input signal. A frequency band dividing section divides the signal of each block into a plurality of frequency bands. A bit allocating section obtains a masking threshold value-to-noise ratio of each frequency band from the magnitude of the power of each frequency band reflecting a psychoacoustic characteristic, and determines the number of quantization bits to be allocated to each frequency band based on the magnitude of the masking threshold value-to-noise ratio. A quantizing section generates a code string by quantizing the signal while allocating a specified amount of bits to each frequency band based on information from the bit allocating section.

Abstract: A post-filter adapted to be used for a speech synthesizing apparatus includes a filtering unit for filtering a synthesized signal, and a scaling coefficient in accordance with both the synthesized signal and a signal output from the filtering unit. The post filter also includes an amplitude detecting unit for detecting an amplitude of the signal output from the filtering unit and for adjusting a value of the scaling coefficient in accordance with a detected result so that an amplitude of the signal output from the filtering unit is kept within a predetermined amplitude value. The post filter further includes a multiplier for calculating the filtering unit with the adjusted scaling coefficient.

Abstract: In a signal encoding device, a voice signal is divided into subsignals each comprising a predetermined number of successive samples, and data trains are generated by giving initial values to a recurrence equation. The generated data trains are divided into patterns each comprising the same number of samples as the predetermined number. The distance between each pattern produced by the pattern dividing unit and each of the subsignals are calculated. The pattern that provides the smallest distance with respect to each of the subsignals is identified, and the initial value set in the recurrence equation for generation of the data train that constitutes the pattern is output as coded data representing the respective subsignal.

Abstract: A speech analyzing and synthesizing apparatus samples a speech signal and its coding section outputs one or more codes of variable length per sampling according to the differential value between two mutually adjacent sampled signals to represent this differential value. The apparatus also includes a decoding section which decodes the outputted codes to obtain the differential value and a limiting circuit for limiting the number of outputtable codes per sample according to the differential value and codes representing differential values previously outputted from the coding section.