Abstract: An arrangement for tuning a data filter in a mass storage system. The filter cutoff frequency (low pass) may be set as a percentage above or below the incoming data rate to achieve the desired "eye opening" in read data. The frequency of a reference oscillator in a phase-locked-loop (PLL) and the cutoff frequency of the filter is controlled by a common control signal from the PLL. The PLL, locked to a scaled multiple of the data rate, determines the cutoff frequency of the filter.

Abstract: Analog filters may be conveniently implemented in MOS technology by the use of "transconductance cells". Each cell includes stages each having a pair of current paths, with each path comprising a current source and input transistor. The gain of each stage is set by a transistor connected across the current path, with the transconductance of this transistor being controlled by its gate voltage. In the inventive technique, a transconductance cell comprising two input stages utilizes inputs to each input stage that are in-phase rather than complementary, as in prior-art designs. The inputs to the second input stage are then each balanced (out of phase) with respect to the inputs to the first input stage. Higher linearity is obtained, with the common-mode signal being cancelled by the summation of currents supplied by the input stages to the common output stage. A biquadratic filter conveniently implements this technique, with other applications being possible.

Abstract: An operational amplifier and method for making same, with predetermined common mode voltage gain, adapted to form an amplifier and a voltage regulator. The predetermined common mode voltage gain allows for substantially reduced differential mode gain and wider operating bandwidth with little distortion, compared to amplifiers and voltage regulators using operational amplifiers of the prior art. Further, examples of operational amplifiers, having the reduced differential mode gain and predetermined common mode gain, are given for implementation in CMOS and bipolar technologies.

Abstract: A digital-to-analog signal converter (1000) provides an analog output signal by subtracting bit currents reflecting a digital input signal from a constant current source (1004, 1018-1022) at a current summer (1003), with the difference current being applied to a constant load. The subtracting of the current, rather than switching the current, avoids the modulation of an associated power source since the total current demand remains the same. In that low power operation is possible, the converter is particularly suited for use in an arrangement where only a low level of operating current is available from a power source.

Abstract: A power supply circuit having a higher power factor and decreased current crest factor. The circuit preferably comprises an input circuit for receiving an input AC voltage and rectifying this voltage and an output circuit for providing a DC output voltage. A pulse-width-modulation circuit intercouples between the input and output circuits and includes a controlled circuit adapted to pass input AC current in pulse-wide increments with the pulse-width varying in inverse proportion to the AC voltage. In this manner, when the instantaneous AC voltage is low, the pulse widths are wider and conversely when the voltage is high, the pulse widths are narrower. In one version of the invention, the pulse width modulation is carried out by a programmed variable ratio transformer.

Abstract: In a multifrequency generator providing tone signaling for a telephone, the common switching functions are performed by solid state switching circuitry (1200). Improved signal transfer between the telephone line and transmit and receive transducer of the telephone is provided by arranging the solid-state transmit and receive switches (1201, 1401) in a gain configuration to increase the level of the speech signal. The tone signals are digitally synthesized and use an integrated R-C oscillator (600) as a reference. Button down and button up debouncing of a contact closure signal from a single contact per button keypad is provided.

Abstract: In a multifrequency generator providing tone signaling for a telephone, the common switch functions are performed by solid-state switching circuitry (12). The dc drive current level to the solid-state switching circuitry varies with the loop length of the telephone line such that saturation of switching transistors (405, 409, 410, 508 and 518) contained therein will be maintained on longer loops even with the corresponding decrease in operating current available from a central office. In the speech mode, the appropriate switching transistors are driven with a a high impedance current sources (505-507 and 514-517) thereby preventing an unacceptable shunt degradation of the speech signals. Similarly, in the dial mode, a high impedance current sink (406 and 407) drives the appropriate switching transistors, thus preventing shunt degradation of the tone signals.