Center frequency and Q tuning of biquad filter by amplitude-limited oscillation-based calibration
AssigneeQUALCOMM Incorporated
InventorsShuja Andrabi, Rahul Karmaker
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Abstract
Certain aspects of the present disclosure provide methods and apparatus for calibrating a tunable active filter. One example apparatus is a filter circuit that generally includes a tunable active filter comprising at least one amplifier and a first feedback path coupled between an input and an output of the at least one amplifier, the first feedback path comprising at least one switch; and an amplitude limiter coupled to the tunable active filter and comprising at least one transistor disposed in a second feedback path coupled between the input and the output of the at least one amplifier.
Claims21
A filter circuit comprising:
- a tunable active filter comprising at least one amplifier and a first feedback path coupled between an input and an output of the at least one amplifier, the first feedback path comprising at least one switch and the tunable filter being configured to generate an oscillating signal when the at least one switch is open;
- and
- an amplitude limiter coupled to the tunable active filter and comprising at least one transistor disposed in a second feedback path coupled between the input and the output of the at least one amplifier.
A filter circuit comprising:
- a tunable active filter comprising at least one amplifier and a first feedback path coupled between an input and an output of the at least one amplifier, the first feedback path comprising at least one switch;
- and
- an amplitude limiter coupled to the tunable active filter and comprising at least one transistor disposed in a second feedback path coupled between the input and the output of the at least one amplifier, wherein:
- the tunable active filter comprises a differential tunable active filter having at least one differential amplifier with first and second inputs and first and second outputs;
- the amplitude limiter comprises first and second amplitude-limiting circuits;
- the first amplitude-limiting circuit is coupled between the first input and the first output of the at least one differential amplifier;
- and
- the second amplitude-limiting circuit is coupled between the second input and the second output of the at least one differential amplifier.
A method for calibrating a tunable active filter comprising at least one amplifier, the method comprising:
- generating an oscillating signal with the tunable active filter by opening at least one first switch in a first feedback path coupled between an input and an output of the at least one amplifier;
- and
- limiting the amplitude of the oscillating signal generated by the tunable active filter by enabling an amplitude-limiting circuit coupled to the tunable active filter, the amplitude-limiting circuit comprising at least one transistor disposed in a second feedback path coupled between the input and the output of the least one amplifier.
Dependencies are inferred from the claim text.