Input filter circuit for an operational amplifier
View Patent ↗A controller that is linearly responsive to an input voltage provides continuously adjustable control of the width of a periodically repeating digital pulse, thereby achieving a linear voltage to duty-cycle ratio transfer function. The circuit of the present invention includes a master clock input, a ratio control voltage input, a controlled duty cycle clock output, a high gain amplifier configured as an integrator having differential inputs, each equipped with a low pass filter, a controlled current source, a resettable timing capacitor, a threshold detector and a reference pulse generator.
1. An improved input filter circuit for an operational amplifier, said operational amplifier having an inverting input, a non-inverting input, and an output, the improved filter circuit comprising:
a first resistor:
a second resistor connected in series with said first resistor;
said second resistor connected to the inverting input of the operational amplifier;
a first capacitor connected between the output of the operational amplifier and a mid-point between said first and second resistors; and
a third resistor and a second capacitor connected in series between the inverting input of the operational amplifier and the output of the operational amplifier.