Highly-linear continuous-time filter for a 3-volt supply with PLL-controlled resistor and digitally-controlled capacitor
US6097244A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Dec 17, 1998 |
| Grant date | Aug 1, 2000 |
| Priority date | — |
| Expiry date | Dec 17, 2018 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03L7/06
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
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 ad…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.