US 5,966,046 AGranted

Large swing wide band programmable active filter

AssigneeFairchild Semiconductor Corporation

InventorsIgnatius S. A. Bezzam, David W. Ritter

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Abstract

A wide-band, high-order, programmable video filter is implemented using transimpedance-based active integrators. An input voltage which may for instance represent a composite video signal is converted to a current in a linear manner using resistors and provided to a current amplifier at low impedance virtual ground nodes. The current is multiplied by a gain factor .beta..sub.R within the current amplifier and supplied to integrating capacitors connected in a feedback configuration around a high input impedance differential amplifier to establish an integrated differential voltage output. The transimpedance-based active integrators may be interconnected to realize wide-band, high-order video filters suitable for use in accordance with CCIR 601 standards. Input voltage swings are not restricted by a transistor's limited range of linear operation or voltage swing limitations of internal nodes but rather may allowed to swing as long as the bias currents sustain input current excursions. Thus, pre-filter attenuation and post-filter amplification is not required, thereby allowing CCIR 601 standard compliant video filters to be fabricated, in accordance with the present invention, as a single chip IC.

Claims3

Dependent claims

A filter comprising:

a filter input port;
a filter output port;
a first resistive element coupled to said filter input port;
a second relative element coupled to said filter output port;
a differential transimpedance amplifier comprising:
first and second supply voltages;
an amplifier input port coupled to both said resistive elements;
a first transistor having an emitter coupled to said amplifier input port, a collector coupled to said first supply voltage, and a base;
a second transistor having an emitter coupled to said amplifier input port, a collector coupled to said first supply voltage, and a base coupled to said base of said first transistor;
a third transistor having an emitter coupled to said amplifier input port, a collector coupled to said second supply voltage, and a base;
a fourth transistor having an emitter coupled to said amplifier input port, a collector coupled to said second supply voltage, and a base coupled to said base of said third transistor;
and
an amplifier output port coupled to receive first and second signals provided by said collectors of said first and second transistors, respectively;
a first capacitive element coupled between said filter input port and said amplifier output port;
and
a second capacitive element coupled between said filter output port and said amplifier output port.

13 more elements

Dependencies are inferred from the claim text.