Variable gain transconductance amplifier and variable bandwidth filter
AssigneeMotorola, Inc.
InventorBarry L. Jason
Life of this patent
Estimating the term…
Abstract
A variable gain transconductance amplifier wherein complimentary input followers are used in conjunction with the multiplier to provide a high input impedance. A pair of multiplier input devices are embedded in the input followers to reduce the supply voltage used by the multiplier and to improve signal handling capability while reducing the supply voltage required. Further, these variable gain transconductance amplifiers are used in active filters to provide adjustment of the bandwidth without affecting the center frequency.
Claims9
An active band pass filter with variable bandwidth comprising:
- first, second, and third variable gain transconductance amplifiers each having at least first and second differential inputs and an output;
- a first junction coupled to the output of said first and second amplifier and to a first selected one of the differential input of said third amplifier;
- a second junction, coupled to the output of said third amplifier and to the second differential input of said second amplifier, the first differential input terminal of said second and the second differential input of said third amplifier being coupled to a reference potential;
- first and second capacitors each having a terminal coupled to said first and second junctions, respectively, and each having a second terminal coupled to the reference potential.
A low supply voltage, high swing input signal, variable gain transconductance amplifier, comprising:
- a pair of complimentary input follower circuits, having complimentary inputs;
- an element coupled to each of said follower circuits to provide a signal current in said element in response to a differential input voltage applied to the complimentary inputs of said follower circuits, said signal current element producing differential currents in each of said follower circuits;
- a multiplier having a pair of input devices, one each coupled into and forming a common component with each of said follower circuits, said input devices sensing the differential current flowing into follower circuits,
- said input devices of said multiplier including a pair of transistors having common connected bases and the multiplier further including a differential pair of transistors having common connected emitters;
- said pair of complimentary input follower circuits including a pair of opposite conductivity transistors connected with the base of a first transistor of said pair forming one of the complimentary inputs, the emitter of the second transistor of said pair being connected to the element, and the emitter of the first transistor being connected to the base of the second transistor;
- and
- a first biased current source coupled to the complimentary input follower circuits and a second biased current source coupled to the multiplier, said second biased current being variable to vary the transconductive gain of said amplifier, the ratio of the first biased current to the second biased current setting the transconductive gain if the amplifier.
Dependencies are inferred from the claim text.