United States of America As Represented by the Secretary of the Air Force

Bell Telephone Laboratories

At&t Bell Laboratories

Kenneth R Laker

Paul E Fleischer

Andrew J Slobodnik, Jr

Apparajan Ganesan

Paul H Carr

Aristides Antony Yiannoulos

Jimmy Tow

Thomas L Szabo

Alan J Budreau

James P Ballantyne

A switched capacitor oscillator is constructed by providing a damped resonator network with a comparator as a nonlinear feedback element by connecting the input of the comparator to the output of a first operational amplifier of the resonator network and connecting the output of the comparator to the input of the resonator network. The comparator thus becomes a saturable positive feedback element for the resonator network. Also disclosed is a startup network for the oscillator and an input network which derives an input from a reference voltage in order to eliminate supply voltage noise and provide precision control of amplitude.

Switched capacitor oscillator formed by a damped resonator with

A capacitor-resistor-capacitor (CRC) element for active filter realization, which is fully integrable and compatible with MOS technology, is described. The incorporation of the CRC element in a semiconductor integrated circuit active filter also is described. The structure of the CRC filter element is closely analogous to a depletion mode MOS field effect device, except that the channel zone 26 is doped to a level which substantially precludes conductivity modulation at the usual operating voltages. However, the doping level is such as to enable the use of the channel zone as a semiconductor resistance element. Thus, the N-channel CRC element realized in the NMOS technology comprises a first capacitance composed of the gate 27, gate dielectric 38, and resistive channel 26, paralleled by the resistive channel 26 itself constituting a resistor, and then the underlying PN junction capacitance between the N-type resistive channel 26 and the underlying P-type semiconductor body portion 21. An active low-pass filter consists of two CRC elements and an operational amplifier and utilizes the positive feedback principle.

Integrated CRC filter circuit

Because of the very large variety of useful filter configurations, it is highly desirable to have a generalized circuit topology from which all specific filters can be derived. A generalized switched-capacitor biquadratic active filter comprises a pair of operational amplifiers (10, 11), each of which has an unswitched feedback capacitor (D, B) connected between its output port (3, 3') and its inverting input port (1, 1'). A third through-switched capacitor (C) provides feedback between the output port (3') of the second amplifier (11) and the inverting input port (1) of the first amplifier (10). A diagonally-switched capacitor (A) couples the output port (3) of the first amplifier (10) to the inverting input port (1') of the second amplifier (11). The noninverting input ports (2, 2') of the two amplifiers are connected to signal ground. The filter input terminal (5) is connected to the inverting input ports (1, 1') of each amplifier by an input circuit including a parallel array of an unswitched capacitor, a diagonally-switched capacitor, and a through-switched capacitor (L, H, G and K, J, I). Damping is provided by either a through-switched capacitor (F) connected in parallel with feedback capacitor (B), or by a unswitched capacitor (E) connected in parallel with through switched feedback capacitor (C).

Generalized switched-capacitor active filter

An enhanced pole quality factor (Q) notch filter section circuit includes an active biquadratic notch filter section and a pole quality factor enhancement amplifier responsive to the output of the biquadratic notch filter section for providing at the input of the biquadratic notch filter section negative feedback in pass and stop bands of frequencies and positive feedback in the transition range of frequencies between the pass and stop bands of frequencies.

Pole quality factor (Q) enhancement technique for notch filters

Passband distortion due to mass loading in withdrawal weighted surface acoustic wave transducers is substantially reduced by a thinning technique in which interdigital transducer electrodes are selectively withdrawn to synthesize a response function H.sub.o '(N). H.sub.o '(N) is a modified response function that has been scaled from a desired response function H.sub.o (N) by a thinning factor THIN. THIN is a positive, non-zero constant with a maximum value of unity. Thinned withdrawal weighted transducers fabricated in accordance with the technique have electrode weights that are normalized to less than unity and achieve mass loading reduction with a minimum amount of degradation of the desired response function.

Thinned withdrawal weighted surface acoustic wave interdigital

A surface acoustic wave bandpass filter having a flat frequency response in the passband and an exponentially decaying out-of-band response is realized by designing its transducer electrodes to have an appropriate number of discretely apodized interdigital fingers. The apodization or overlap coefficients H.sub.o (N) of adjacent fingers are determined from an analytically derived expression that incorporates factors for the filter time length parameter, the filter center frequency, bandwidth, transition bandwidth falloff, and a ripple reduction parameter.

Surface acoustic wave filter

The input transducers of a multichannel surface acoustic wave device are electrically connected in a series or series-parallel circuit arrangement and are connected to a single channel electromagnetic wave transmission line through an inductor. The inductance value of the inductor is chosen such that minimum transducer insertion loss is achieved at the center frequency of the midband channel. The circuit arrangement is selected which achieves optimum coupling to the midband channel subject to the constraint that the insertion losses of all the remaining channels, measured at their respective center frequencies, lie at or near the above optimum value within an acceptable prespecified margin.

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Staten Island, NY, United States of America

Kenneth R Laker