Zero time constant filter using sample-and-hold technique

Claim 2

In a method of converting a periodic, time-varying signal to a DC signal having a magnitude of the peak value of said timevarying signal for each period, the steps comprising: detecting the point in time at which said first signal reaches a peak for each period by differentiating said time-varying signal; and detecting the zero-crossing time of said differentiated signal; sampling said first signal at said point in time when it reaches a peak; and, generating a continuous DC output signal substantially equal to the peak value of said first signal.

Claim 3

An electronic near zero time constant filter circuit for receiving periodic time-varying signals and producing a DC signal having a magnitude related to the peak value of the time-varying signal for each period thereof, comprising: peak-detecting means adapted to receive said periodic time-varying input signals and to determine the peak value thereof, including: a differentiating circuit receiving the input signals and producing a differential signal; and a zero-crossing detector connected to receive the differential signal and to produce a sample signal when the differential signal crosses zero going from one given polarity to the other; sample-and-hold means adapted to supply a steady DC output signal equal to a sampled input signal; switching means operated by the sample signal and interconnecting the input of said filter circuit and the input to said sample-and-hold means; and, means interconnecting the sample signal output of said peak-detecting means and said switching means, said means adapted to actuate said switch as said time-varying signal reaches a peak value of one polarity, whereby said switching means conducts the peak value of said time-varying signal to the input of said sample-and-hold means.

Claim 4

An electronic near zero time constant filter circuit for receiving periodic time-varying signals and producing a DC signal having a magnitude related to the peak value of the time-varying signal for each period thereof, comprising: peak-detecting means adapted to receive said periodic time-varying input signals and to determine the peak value thereof, including: a differentiating circuit receiving the input signals and producing a differential signal; and a zero-crossing detector connected to receive the differential signal and to produce a sample signal when the differential signal crosses zero going from one given polarity to the other; sample-and-hold means adapted to supply a steady DC output signal equal to a sampled input signal; switching means operated by the sample signal and interconnecting the input of said filter circuit and the input to said sample-and-hold means; and, means interconnecting the sample signal output of said peak-detecting means and said switching means, said means adapted to actuate said switch as said time-varying signal reaches a peak value of one polarity, whereby said switching means conducts the peak value of said time-varying signal to the input of said sample-and-hold means.

Claim 5

The apparatus of claim 2 wherein said peak-detecting means comprises: a differentiating circuit including an operational amplifier having a varistor connected between the output of said operational amplifier and its inverting input, and a capacitor connected to said inverting input of said operational amplifier to create high-accuracy zero crossings; a zero-crossing detector connected to the output of said differentiating circuit and adapted to supply an output signal when the output signal of said differentiating circuit crosses zero; and, a one-shot circuit connected to the output of said zero-crossing detector and adapted to supply a uniform output pulse as said sample signal in response to a signal supplied to the input thereof.

Claim 6

The apparatus of claim 3 wherein said switching means comprises a field-effect transistor having a gate electrode and two additional electrodes, said gate electrode being connected to the output of said single-SHOT circuit and the two additional electrodes interconnected between the source of said time-varying signals and the input to said sample-and-hold circuit.

Claim 7

The circuit of claim 4 wherein said sample-and-hold circuit comprises: an operational amplifier haviNg 100 percent feedback between its output and the inverting input thereto and a capacitor coupled between the noninverting input and ground.