High pass switched capacitor filter section
First Claim
1. A high-pass sampled-data filter comprisinga first integrating operational amplifier;
- input means connected to said first operational amplifier for supplying a continuous signal voltage to be filtered, said input means having a first switch means adapted to be connected with and controlled by a first phase of a continuous two-phase alternating clock generator, a first switched capacitor connected to ground and to said input means, and a first gain multiplying capacitor in said input means between said storage capacitor and the input to said first operational amplifier;
a bypass lead connected between the input and output of said first operational amplifier for providing a feedback thereto and containing an alternating second switch means connected to said second clock generator with a second switched capacitor connected to ground and to said switch means so that it is charged during a second clock phase and discharged as a feedback during each first clock phase;
a second integrating operational amplifier;
means for connecting the output of said first operational amplifier to an input of said second operational amplifier including a third switched capacitor and third switch means connected to said clock generator so that said third switched capacitor is charged during each said second clock phase and is discharged to said second operational amplifier during each said first clock phase;
feedback means connecting the output of said second operational amplifier to said input means of said first operational amplifier including a fourth switch means connected to said clock generator, a fourth switched capacitor connected between said fourth switch means and ground, said fourth switch means being connected so that the output of said second operational amplifier is fed back to charge said fourth switched capacitor during each second clock phase and said capacitor is discharged during each first clock phase;
a third integrating operational amplifier;
conductive means for connecting the output of the first operational amplifier to an input terminal of said third operational amplifier including a fifth switch means connected to the second clock phase of said clock generator, a fifth switched capacitor connected to said conductive means and a second gain amplifying capacitor between the fifth switch means and said input terminal;
feedback means connected between the input and output of said third operational amplifier including a sixth switched capacitor and a sixth switch means connected thereto and to said clock generator so that said sixth capacitor is charged during each first phase clock cycle and is discharged to feedback during each second phase clock cycle.
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Abstract
A high-pass switched capacitor biquadratic filter based on the bilinear z-transform. The filter comprises first and second integrating operational amplifiers connected in series and in combination with a third operational amplifier that serves as a sample and hold and also generates one simple pole and zero pair in the circuit transfer function thereby enabling the circuit to provide for a high degree of filter efficiency in a preselected frequency range. The operational amplifiers are connected to and operate in cooperation with capacitors of a predetermined size which are switched on and off continuously by two phase clock signals supplied to the circuit. The loss characteristic of the filter can be programmed by varying the clocking frequency. Higher order filters can be obtained by the tandem connection of second order circuit sections followed by one or more first order pole-zero section.
136 Citations
8 Claims
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1. A high-pass sampled-data filter comprising
a first integrating operational amplifier; -
input means connected to said first operational amplifier for supplying a continuous signal voltage to be filtered, said input means having a first switch means adapted to be connected with and controlled by a first phase of a continuous two-phase alternating clock generator, a first switched capacitor connected to ground and to said input means, and a first gain multiplying capacitor in said input means between said storage capacitor and the input to said first operational amplifier; a bypass lead connected between the input and output of said first operational amplifier for providing a feedback thereto and containing an alternating second switch means connected to said second clock generator with a second switched capacitor connected to ground and to said switch means so that it is charged during a second clock phase and discharged as a feedback during each first clock phase; a second integrating operational amplifier; means for connecting the output of said first operational amplifier to an input of said second operational amplifier including a third switched capacitor and third switch means connected to said clock generator so that said third switched capacitor is charged during each said second clock phase and is discharged to said second operational amplifier during each said first clock phase; feedback means connecting the output of said second operational amplifier to said input means of said first operational amplifier including a fourth switch means connected to said clock generator, a fourth switched capacitor connected between said fourth switch means and ground, said fourth switch means being connected so that the output of said second operational amplifier is fed back to charge said fourth switched capacitor during each second clock phase and said capacitor is discharged during each first clock phase; a third integrating operational amplifier; conductive means for connecting the output of the first operational amplifier to an input terminal of said third operational amplifier including a fifth switch means connected to the second clock phase of said clock generator, a fifth switched capacitor connected to said conductive means and a second gain amplifying capacitor between the fifth switch means and said input terminal; feedback means connected between the input and output of said third operational amplifier including a sixth switched capacitor and a sixth switch means connected thereto and to said clock generator so that said sixth capacitor is charged during each first phase clock cycle and is discharged to feedback during each second phase clock cycle. - View Dependent Claims (2, 3, 4)
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5. A sampled-data high pass filter comprising
a first operational amplifier having its own feedback loop; -
input means to said first operational amplifier; a second operational amplifier, means connecting the output of said first operational amplifier to the input of said second operational amplifier; means for providing a feedback loop from the output of said second operational amplifier to said input means of said first operational amplifier; a third operational amplifier having its own feedback loop; means connecting the output of the first operational amplifier to the input of said third operational amplifier; a plurality of switched capacitors in said feedback loops and said connection means; switch means operated by a continuous two-phase clock generator for controlling the charging and discharging of said switched capacitors so that said filter produces a predetermined filter characteristic with a third order transfer function. - View Dependent Claims (6, 7, 8)
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Specification