Variable admittance circuit

摘要

A programmable variable admittance circuit may be used in a programmable filter or a variable gain amplifier in a number of different applications including tuners and other RF receiver circuits. A variable admittance circuit and operation is described including a number of switchable admittance elements arranged in parallel branches. The variable admittance circuit requires fewer transitions to change between successive admittance values than a binary weighted circuit and fewer branches for implementation then a thermometry admittance circuit.

主权项

1. A variable admittance circuit comprising a plurality of admittance elements arranged in parallel branches, the plurality of admittance elements comprising:
a fixed admittance element having an admittance value Y0, a sequence of at least three switchable admittance elements having respective admittance values Y1 in a geometric sequence with a common ratio r and first value Y1 given byY1=Ymin*(r-1r)=Y0*(r-1)wherein the variable admittance circuit is operable to vary the total admittance between a minimum admittance value Ymin and a maximum admittance value Ymax in steps by switching the switchable admittance elements thereby selecting or unselecting the switchable admittance elements and wherein
the common ratio is less than two and greater than a maximum step, and the at least three switchable admittance elements comprise a first switchable admittance element having an admittance value Y1, a second switchable admittance element having an admittance value Y2, and a further switchable admittance element of rank i having an admittance value of K*(Y1+Y2), wherein K is a number in the range of 0.8 to 1.05.