Self-calibrated, broadband, tunable, active filter with unity gain cells for multi-standard and/or multiband channel selection

A circuit comprising:

• a filter, said filter in turn comprising:
• N unity gain amplifiers, N being at least two, each of said N unity gain amplifiers having a pair of differential input terminals and a pair of differential output terminals, said pair of differential output terminals of a last one of said N unity gain amplifiers comprising filter differential output terminals;
• a pair of filter differential input terminals;
• a first pair of variable resistances coupling said pair of filter differential input terminals to said pair of differential input terminals of a first one of said N unity gain amplifiers;
• N−1 pairs of variable resistances coupling said pairs of differential output terminals of each of said N unity gain amplifiers, other than said last one of said N unity gain amplifiers, to said pairs of differential input terminals of its downstream neighbor;
• N−1 pairs of variable capacitances coupling said pairs of differential input terminals of each of said N unity gain amplifiers, other than said last one of said N unity gain amplifiers, to said pairs of differential output terminals of its downstream neighbor;
• and
• a variable capacitance coupling said pair of differential input terminals of said last one of said N unity gain amplifiers to each other;
• wherein said N unity gain amplifiers each in turn comprise:
• a linearized operational transconductance amplifier stage coupled to a corresponding pair of said differential input terminals;
• and
• a unity gain buffer with feedback interconnected between said linearized operational transconductance amplifier stage and a corresponding pair of said differential output terminals;
• an oscillator, said oscillator in turn comprising:
• N greater than unity gain amplifiers, N being at least two, each of said N greater than unity gain amplifiers having a pair of differential input terminals and a pair of differential output terminals;
• a first pair of oscillator variable resistances coupling:
• a negative one of said pair of differential output terminals of a last one of said N greater than unity gain amplifiers to a positive one of said pair of differential input terminals of a first one of said N greater than unity gain amplifiers, and
• a positive one of said pair of differential output terminals of said last one of said N greater than unity gain amplifiers to a negative one of said pair of differential input terminals of said first one of said N greater than unity gain amplifiers;
• N−1 pairs of oscillator variable resistances coupling said pairs of differential output terminals of each of said N greater than unity gain amplifiers, other than said last one of said N greater than unity gain amplifiers, to said pairs of differential input terminals of its downstream neighbor;
• N−1 pairs of oscillator variable capacitances coupling said pairs of differential input terminals of each of said N greater than unity gain amplifiers, other than said last one of said N greater than unity gain amplifiers, to said pairs of differential output terminals of its downstream neighbor;
• and
• an oscillator variable capacitance coupling said pair of differential input terminals of said last one of said N greater than unity gain amplifiers to each other;
• wherein said N greater than unity gain amplifiers each in turn comprise:
• a linearized operational transconductance amplifier stage coupled to a corresponding pair of said differential input terminals;
• and
• a unity gain buffer with feedback interconnected between said linearized operational transconductance amplifier stage and a corresponding pair of said differential output terminals;
• and
• a control arrangement configured to:
• compare a frequency of oscillation of said oscillator to a reference;
• and
• exert common control over said first pair of variable resistances, said N−1 pairs of variable resistances, said N−1 pairs of variable capacitances, said variable capacitance coupling said pair of differential input terminals of said last one of said N unity gain amplifiers to each other, said first pair of oscillator variable resistances, said N−1 pairs of oscillator variable resistances, said N−1 pairs of oscillator variable capacitances, and said oscillator variable capacitance coupling said pair of differential input terminals of said last one of said N greater than unity gain amplifiers to each other, so as to match said frequency of oscillation of said oscillator to said reference and control bandwidth of said filter.