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 Title: |
US6097244:
Highly-linear continuous-time filter for a 3-volt supply with PLL-controlled resistor and digitally-controlled capacitor
[ Derwent Title ]
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| Country: |
US United States of America
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| Inventor: |
Chen, Xiaole; Milpitas, CA
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| Assignee: |
Centillium Communications, Inc., Fremont, CA
other patents from CENTILLIUM COMMUNICATIONS, INC. (771192) (approx. 9)
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| Published / Filed: |
2000-08-01
/ 1998-12-17
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| Application Number: |
US1998000215508
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| IPC Code: |
Advanced:
H03H 11/04;
H03H 19/00;
H03J 7/04;
H03L 7/06;
Core:
H03J 7/02;
more...
IPC-7:
H04B 1/10;
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| ECLA Code: |
H03H11/04; H03H19/00B; H03J7/04; H03L7/06;
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| U.S. Class: |
Current:
327/553;
327/308;
327/552;
327/556;
327/557;
327/558;
Original:
327/553;
327/552;
327/308;
327/558;
327/557;
327/556;
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| Field of Search: |
327/308,552,553,362
330/305,303
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| Priority Number: |
| 1998-12-17 |
US1998000215508 |
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| Abstract: |
A continuous-time filter is highly linear even when used with reduced 3-volt power supplies. In each stage of a multi-stage ladder network, resistor networks are attached to each input of a differential op amp. Each resistor network uses fixed resistors in series between the inputs and an intermediate node, and a fixed input resistor between the intermediate node and the op-amp input. The fixed input resistor improves linearity compared with a linear transistor. A transistor connects the internal node to ground, acting as a variable resistor to adjust the equivalent resistance of the resistor network. A control voltage applied to the gate of the transistor is generated by an analog control loop. The control voltage is the voltage input to a voltage-controlled oscillator (VCO) in a phase-locked loop (PLL). The analog PLL control loop adjusts the control voltage and the resistance continuously as the filter operates. A voltage comparator detects when the control voltage is out of a range, activating a calibration signal. Filtering stops and a digital successive-approximation register adjusts capacitances of feedback capacitors around the op amps. The capacitance in the VCO is also adjusted, changing the control voltage. Capacitance converges to the desired value by comparing the control voltage to a mid-range target voltage.
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| Attorney, Agent or Firm: |
Auvinen, Stuart T. ;
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| Primary / Asst. Examiners: |
Lam, Tuan T.; Nguyen, Hiep
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| INPADOC Legal Status: |
Show legal status actions
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| Family: |
None
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First Claim:
Show all 18 claims |
I claim:
1. A highly-linear ladder filter that adjusts resistance comprising:
- a plurality of filter stages, each filter stage having:
- an op amp with a pair of op-amp inputs, for amplifying a voltage difference between the pair of op-amp inputs to generate op-amp outputs;
- a pair of feedback capacitors, each feedback capacitor connecting an op-amp output to an op-amp input;
- a pair of resistor networks, each resistor network connecting a stage input to an op-amp input with an equivalent resistance, the equivalent resistance being continuously adjusted by a control voltage;
- wherein each resistor network includes:
- a first fixed resistor, connecting the stage input to an intermediate node;
- a fixed input resistor, connecting the intermediate node to the op-amp input;
- a variable resistor, connecting the intermediate node to a ground node, the variable resistor having a resistance controlled by the control voltage;
- wherein the variable resistor is a transistor biased in a linear region of operation by the control voltage applied to a gate of the transistor, wherein a drain of the transistor is connected to the intermediate node and wherein a source of the transistor is connected to the ground node: and
- an analog control loop for generating the control voltage
- whereby the control voltage adjusts channel resistance through the transistor and whereby linearity is improved by using the fixed input resistor connected to the op-amp input while the equivalent resistance of the resistor network is adjusted with the control voltage by the variable resistor to the ground node.
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| Background / Summary: |
Show background / summary
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| Drawing Descriptions: |
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| Description: |
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| Forward References: |
Show 10 U.S. patent(s) that reference this one
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| Foreign References: |
None
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| Other Abstract Info: |
DERABS G2000-601190
DERABS G2000-601190
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| Other References: |
Banu, M and Tsividis, Y., "An Elliptic Continuous-Time CMOS Filter with On-Chip Automatic Tuning" IEEE JSSC vol. SC-20, No. 6, pp 1114-21, Dec. 1985.
(8 pages)
Cited by 6 patents
Moon and Song, "Design of a Low-Distortion 22-KHz Fifth-Order Bessel Filter" IEEE JSSC vol. 28, No. 12, pp 1254-64, Dec. 1993.
(11 pages)
Cited by 8 patents
[ISI abstract]
Durham and Redman-White, "Integrated Continuous-Time Balanced Filters for 16-b DSP Interfaces" IEEE JSSC vol. 28, No. 7, pp 835-39, Jul. 1993.
(5 pages)
Cited by 4 patents
[ISI abstract]
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