Abstract: A digital high-pass filter derived from a digital low-pass filter of conventional design. The digital low-pass filter periodically calculates respective low-pass filter output values. Corresponding high-pass filter output values are then calculated by subtracting the low-pass filter output values from input samples provided by digitizing an input signal. The high-pass filter output values are then used to generate samples which are applied to a digital-to-analog converter for outputting a high-pass filtered replica of the input signal. The digital high-pass filter compensates for sudden, relatively large changes in the input signal by comparing the low-pass filter output value to the input sample and, in the event that there is a large discrepancy therebetween, setting the low-pass filter output value to the input sample before calculating the high-pass filter output value.

Abstract: A circuit arrangement with an adjustable amplitude-frequency response between an input signal terminal and an output signal terminal can be changed over simply between a fourth-order high-pass or low-pass characteristic and a second-order all-pass characteristic. The circuit includes first and third filters each with a filter function F, a second filter with a filter function G, a plurality of coefficient sections and first and second summing stages all coupled together so that the circuit has a transfer function A between the input signal terminal and the output signal terminal with a component complying withA=(C+(1-C).multidot.F-2.multidot.C.multidot.G).multidot.(C(1-C).multidot.F) ,whereF=FN=1/(1+a.multidot.s+b.multidot.s.sup.2)orF=FH=b.multidot.s.sup.2 /(1+a.multidot.s+b.multidot.s.sup.2)represents a first filter function with a second-order high-pass or a low-pass characteristic andG=a.multidot.s/(1+a.multidot.s+b.multidot.s.sup.

Abstract: Method and apparatus automatically select, in a playback mode, a noise reduction circuitry of a noise reduction system by which a middle-to-high frequency signal of a low level included in a recording signal is compressed in dynamic range for recording and the compressed middle-to-high frequency signal is expanded in dynamic range in the playback mode, thereby suppressing middle to high frequency noises in the reproduction signal. A level difference .DELTA.L between the maximum and minimum signals of the low frequency component in the reproduction signal and a level difference .DELTA.H between the maximum and minimum signals of the middle-to-high frequency component in the reproduction signal are obtained. While comparing the magnitudes of the two level differences obtained, the selection of an appropriate noise reduction circuitry is performed so that the two level differences are made almost equal to each other.

Abstract: An electronic filter for passing predetermined frequencies includes resistive and capacitive components that need not be rated to handle the input voltage. An input signal is converted to a second signal that is proportional to the logarithm of the input signal (and therefore of much smaller magnitude than the input signal), and then low, high, bandpass filtered with an RC filter. The filtered signal is reconverted to an output signal that is proportional to the inverse logarithm of the filtered signal. The filter may be embedded in a current mirror that may be used in telephone system subscriber line interface circuit.

Abstract: In a remote control system, a receiver demodulates an incoming signal that is typically RF into a digital signal. Signal shaping is required in order to transform small AC signal variations into clean, full-level digital signals. An increased sensitivity signal shaper circuit uses AC coupling with a fully differential architecture. A capacitor couples the input signal to a fully differential operational amplifier where a feedback capacitor sets the gain and a switched capacitor sets the time constant and operating point. The differential operational amplifier has a differential output that is fed into a single ended output comparator that is followed by a schmidt trigger which restores the signal to full logic levels.

Abstract: A waveform shaping circuit shapes a waveform by comparing an output signal generated by an electromagnetic coil in response to a change in an incident magnetic flux to a reference voltage in a comparator. The circuit prevents waveform shaping error due to rapid fluctuations in the output signal. The waveform shaping circuit includes a high-pass filter that removes low-frequency components having frequencies not higher than a cut-off frequency from the output signal of the electromagnetic coil and that has at least two different attenuation characteristics with respective cut-off frequencies, a voltage limiting circuit for switching between the attenuation characteristics of the filter in response to the amplitude of the output signal of the electromagnetic coil by limiting the amplitude of the output signal to a maximum voltage, and a comparator for comparing the filtered output signal with a reference voltage and generating a shaped output signal in response.

Abstract: A circuit for an inductive current sensor that optimizes waveform fidelity of the inductively sensed current for non-sinusoidal currents is claimed. The circuit employs a high gain op amp to sum the inputs of a feedback capacitor and other feedback impedance components including a second op amp and a capacitor, the values of which are selected to provide a double pole roll-off with a gain peaking Q of between 1 and 10, and an impedance which at the low corner frequency is approximately equal to that of the feedback capacitor. Above the low corner frequency of the sensor, the impedance is sufficiently high to have substantially no effect on the circuit and which decreases below the low corner frequency.

Abstract: A phase shifter includes first and second single pole double throw switches, a low-pass filter, and a high-pass filter. The first switch has an input terminal and first and second output terminals, and the second switch has first and second input terminals and an output terminal. The low-pass filter is interposed between the first output terminal of the first switch and the first input terminal of the second switch and includes FETs as capacitors. The high-pass filter is interposed between the second output terminal of the first switch and the second input terminal of the second switch and includes a plurality of FETs as capacitors. The input terminal of first switch and the output terminal of the second switch are an input terminal and an output terminal of the phase shifter, respectively. Each of the high-pass filter and the low-pass filter produces two different phase quantities by the on-off switching of the FETs. Therefore, four different phase quantities are obtained in the phase shifter, i.e.

Abstract: An embodiment of the present invention comprises a series pass transistor with its emitter arranged to receive a source of DC power, its collector arranged to supply a DC load, and its base connected to the junction of a capacitor to ground and an inductor to the collector. An output capacitor from the collector to ground is alternatively included. In a second embodiment of the present invention, an operational amplifier is inserted in the base circuit to increase the effective circuit gain.