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Voltage tunable active inductorless filter

Imported: 23 Feb '17 | Published: 22 Oct '02

Leonard Forbes

USPTO - Utility Patents

Abstract

A monolithic active frequency selection circuit includes an input presenting a frequency-dependent impedance and a first gain block configured to provide less than unity voltage gain, a high input impedance and a low output impedance. An output of the first amplifier is coupled to the frequency selection circuit input. The frequency selection circuit includes a first phase shifter that, in one aspect, is formed by a first capacitor coupled between the first port and a reference voltage. The frequency selection circuit also includes a second amplifier configured to provide greater than unity voltage gain. The second amplifier has an input coupled to the output of the first amplifier and an output coupled to the input of the first amplifier. The frequency selection circuit further includes a second phase shifter, which may be formed from a capacitor coupled between the output of the second amplifier and a reference voltage. The first and second amplifiers and the first and second phase shifters are coupled in a loop such that the frequency dependence of an impedance presented at the output of the first amplifier emulates the impedance of a parallel RLC tank circuit, providing a Q on the order of ten at a center frequency

o, of several hundred megahertz. The output of the second amplifier may be used to provide a high Q, tuned transimpedance amplification function relative to the input.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic diagram of an inductorless, voltage-tunable filter circuit, in accordance with an embodiment of the present invention.

FIG. 2 is a simplified schematic diagram of the inductorless filter circuit of FIG. 1, showing FETs to realize the current sources and active elements of the circuit of FIG. 1, in accordance with an embodiment of the present invention.

FIG. 3 is a graph of simulated input impedance and transimpedance for the filter circuit of FIG. 2, in accordance with an embodiment of the present invention.

FIG. 4 is a graph showing simulated center frequency

o versus power supply voltage for the circuit of FIG. 2, in accordance with an. embodiment of the present invention.

FIG. 5 is a simplified schematic diagram of another embodiment of an inductorless, voltage-tunable filter circuit, in accordance with an embodiment of the present invention.

FIG. 6 is a simplified schematic diagram of a self-biasing filter circuit that is an embodiment of the filter circuit of FIG. 2, in accordance with an embodiment of the present invention.

FIG. 7 is a simplified block diagram of a radio including tuned circuits using the circuits of FIG. 1,

2,

5 or

6, in accordance with an embodiment of the present invention.

Claims

1. A monolithic radio frequency circuit comprising:

2. A monolithic radio frequency circuit comprising: