Time constant automatic adjustment circuit for a filter circuit

Claim 2

An automatic adjustment circuit for adjusting the time constant of a filter circuit, the adjustment circuit receiving a reference signal having a predetermined reference voltage, and a clock signal, comprising: integration circuit means for generating an integrated signal having a variable voltage level with periodic peak values, including controllable current generating circuit means, capacitor means for charging a current from the controllable current generating circuit means and switch means for alternately charging and discharging the capacitor means in response to the clock signal; means for comparing the peak values with the reference voltage and generating a control signal for adjusting the time constant of the filter circuit; and feedback circuit means coupled between the comparing means and the controllable current generating circuit means for automatically controlling the control signal.

Claim 3

The automatic time constant adjustment circuit of claim 1 wherein the adjustment circuit also includes amplitude detection means coupled to the capacitor means for detecting the peak voltage of the integrated signal.

Claim 4

The automatic time constant adjustment circuit of claim 2 wherein the adjustment circuit and the filter circuit are in the same integrated circuit chip.

Claim 5

The automatic time constant adjustment circuit of claim 3 wherein the filter circuit includes time constant varying means and the controllable current generating circuit means also includes means corresponding to the time constant varying means of the filter circuit.

Claim 6

The automatic time constant adjustment circuit of claim 4 wherein the each of the time constant varying means is connected to the comparing means for receiving the control signal.

Claim 7

The automatic time constant adjustment circuit of claim 5 wherein the time constant varying means are variable resistance means and the controllable current generating circuit means includes a fixed voltage source and a variable resistance means is connected between the fixed voltage source and the capacitor means.

Claim 8

The automatic time constant adjustment circuit of claim 6 wherein the variable resistance means are MOS transistors.

Claim 9

The automatic time constant adjustment circuit of claim 7 wherein the integration circuit means also includes an operational amplifier in parallel with the capacitor means.

Claim 10

The automatic time constant adjustment circuit of claim 5 wherein the time constant varying means are current conversion circuit means and the controllable current generating circuit means includes a fixed voltage source and a current conversion circuit means is connected between the fixed voltage source and the capacitor means.

Claim 11

An automatic adjustment circuit for adjusting the time constant of a filter circuit, said adjustment circuit receiving a reference signal having a predetermined reference voltage and a clock signal, said automatic adjustment circuit comprising: integration circuit means for generating an integrated signal having a variable voltage level with periodic peak values, said integration circuit means comprising controllable current generating circuit means including a fixed voltage source, capacitor means for charging a current from said controllable current generating circuit means, and switch means for alternately charging and discharging said capacitor means in response to said clock signal; means for comprising said peak values with said reference voltage and generating a control signal for adjusting the time constant of said filter circuit; feedback circuit means coupled between said comparing means and said controllable current circuit generating means for automatically controlling said control signal; and amplitude detection means coupled to said capacitor means for detecting the peak voltage of said integrated signal; wherein said automatic adjustment circuit and said filter circuit are in the same integrated circuit chip; wherein said filter circuit includes time constant varying means and said controller current generating means further comprises means corresponding to said time constant varying means, said time constant varying means comprising current conversion circuit means connected between said fixed voltage source and said capacitor means, current conversion circuit means comprising first and second differential amplifier means connected in series with one another, and first and second current source means for supplying current to said first and second differential amplifier means; and each of said time constant varying means is connected to said comparing means for receiving said control signal.

Claim 12

An automatic adjustment circuit for adjusting the time constant of a filter circuit, said adjustment circuit receiving a reference signal having a predetermined reference voltage and a clock signal, said automatic adjustment circuit comprising: integration circuit means for generating an integrated signal having a variable voltage level with periodic peak values, said integration circuit means comprising controllable current generating circuit means including a fixed voltage source, capacitor means for charging a current from said controllable current generating circuit means, and switch means for alternately charging and discharging said capacitor means in response to said clock signal; means for comprising said peak values with said reference voltage and generating a control signal for adjusting the time constant of said filter circuit; feedback circuit means coupled between said comparing means and said controllable current circuit generating means for automatically controlling said control signal; and amplitude detection means coupled to said capacitor means for detecting the peak voltage of said integrated signal; wherein said automatic adjustment circuit and said filter circuit are in the same integrated circuit chip; wherein said filter circuit includes time constant varying means and said controller current generating means further comprises means corresponding to said time constant varying means, said time constant varying means comprising current conversion circuit means connected between said fixed voltage source and said capacitor means, current conversion circuit means comprising first and second differential amplifier means connected in series with one another, and first and second current source means for supplying current to said first and second differential amplifier means; and each of said time constant varying means is connected to said comparing means for receiving said control signal.

Claim 13

The automatic time constant adjustment circuit of claim 10 wherein each one of the first and second current source means is connected to the comparing means for receiving the control signal.