Abstract: An amplitude-compensated digital-to-analog converter circuit and method of compensation. A unipolar digital-to-analog converter is provided, having a reference connection and a pair of differential, unipolar signal outputs. A sensing circuit senses the common mode component of the differential outputs and produces a common mode signal. A reference source produces a first reference signal, and a differential control amplifier compares the common mode signal to the first reference signal and applies a second reference signal applied to the reference connection of the digital-to-analog converter, thereby stabilizing the reference current for the digital-to-analog converter. The circuit includes a single signal output reference to ground and a multiple-pole low-pass filter.

Abstract: An ac mains test apparatus and method. An audio frequency signal measurement instrument is provided with a circuit for testing the ac mains to which the instrument is connected. The ac mains is internally connected to a coupler which presents an attenuated portion of the ac mains to the low level input of the instrument. A switch is provided for selectively connecting the input either to an audio signal to be measured or to the ac mains portion. The coupler both attenuates the ac mains for input to the instrument and isolates the relatively high ac mains voltage from the low level input.

Abstract: A two-tone test signal method for calibrating a BTSC monitoring system compensates for errors introduced into the monitoring system by unpredictable high frequency components of noise when testing the low frequency performance characteristics of the monitoring system. The two-tone test signal has a low frequency tone and a lower level high frequency tone which overrides the high frequency component of noise. The two-tone test signal is synthesized according to the BTSC specification to produce a "perfect" left-only signal for both tones.

Abstract: A low-distortion transformer-coupled circuit. An amplifier is constructed to have a negative output impedance equal to the resistance of the primary winding of a coupling transformer to which the amplifier is connected thereby cancelling the distortion component produced by the transformer distortion current flowing through the primary winding resistance. The input to the amplifier is thus coupled to the secondary winding of the transformer. A low-frequency feedback circuit is provided between the amplifier output and a non-inverting input thereof. Means is provided for adjusting the negative output impedance of the amplifier to match circuit parameters. Alternatively, the coupling transformer employs two matched primary windings and one secondary winding, and the amplifier is constructed to provide a signal to each primary winding.

Abstract: A dual-stage band pass-band reject filter with feedback. Two state variable band pass filters with identical topology are cascaded as first and second stages. Each stage employs two inverting adders and two inverting integrators in a state variable topology, and each provides a band pass output and a band reject output. Both stages are selectively tuned to the same fundamental frequency. The filter output may be switched from a band pass to a band reject mode. In the band reject mode decreased attenuation of harmonics of the fundamental frequency is achieved by providing a predetermined amount of feedback from either the band reject output or band pass output of the second stage to the input of a respective one of the two adders of the first stage.

Abstract: A state variable oscillator with leveler circuit and with a feedforward circuit for improving the oscillator's rejection of leveler-induced distortion. The feedforward circuit combines a signal representative of a leveler-distorted feedback signal with the main oscillator output to reduce the amount of harmonic distortion, below a certain order, appearing in the output.

Abstract: A multiple-feedback path bandpass/bandreject filter which exhibits a nearly constant Q over a predetermined frequency range, and which is tunable by means of a single variable impedance element is provided. A Thevenin equivalent voltage source is placed in series with the tuning element, wherein the Thevenin voltage is a predetermined constant fractional amplitude of the bandreject output voltage, or its equivalent.

Abstract: An intermodulation test analyzer which automatically determines whether an SMPTE or CCIF intermodulation test is being conducted and switches its output accordingly is disclosed. This is accomplished by sensing the low frequency energy content of the test signal. This energy content is compared to a reference level representative of the low frequency energy content of a typical SMPTE test signal. Therefore, if the low frequency energy content of the input signal is greater than the reference level, the signal is treated as the SMPTE test signal. However, if the low frequency energy content is less than the reference level, the signal is processed as a CCIF test signal.

Abstract: A noise reducing circuit for a frequency discriminator is disclosed for providing a frequency discriminator with reduced sensitivity to noise. Reducing the sensitivity to noise allows certain distortion measurements, such as the well-known SINAD test for broadcast receivers, to be made in the presence of high noise levels.

Abstract: An amplifier is connected between the inverting and non-inverting inputs of an inverting feedback amplifier to substantially reduce distortion caused by inherent physical properties of the semiconductor devices.

Abstract: A feedbeside correction circuit for correcting errors in the frequency response of a wideband amplifier includes a network which models the physical distortion-producing mechanisms of the amplifier semiconductor pn junctions. An input signal is applied simultaneously to the amplifier and to the feedbeside circuit. The feedbeside circuit produces a correction signal which is applied to a summing node and subtracted from the amplifier signal so that the amplifier output is substantially error free. The circuit may be used both for single-ended and differential inputs.