Integrator-filter circuit

A filter arrangement including a plurality of integrator-filter circuits for filtering a push-pull signal, comprising at least two integrator elements, each of said integrator elements comprising:

• two inputs;
• two resistors arranged, respectively, at said two inputs;
• a current multiplier having two signal inputs coupled to said resistors, respectively;
• and
• a push-pull amplifier having an inverting input and a non-inverting input coupled to respective outputs of said current multiplier, said push-pull amplifier having an inverting output fed back to the non-inverting input and a non-inverting output fed back to the inverting input via respective capacitances, the current multiplier having two control inputs for receiving a first and a second control current for adjusting an integration time constant of the integrator element, the second control current flowing, in substantially two halves, through the signal inputs of the current multiplier,
• characterized in that said integrator-filter circuit further comprises means for generating a third control current (I.sub.3) which varies proportionally to the second control current (I.sub.2);
• and
• a respective compensation circuit associated with each integrator element, each of said compensation circuits comprising:
• a first current mirror circuit for generating two substantially equal large equalizing currents in dependence upon the third control current (I.sub.3);
• and
• a second current mirror circuit for generating two equal reference control currents in dependence upon a reference current, means for superimposing said two reference control currents on the two equalizing currents for forming two compensation currents, said two compensation currents being applied to the signal inputs of the current multiplier in the associated integrator element, and means for dimensioning each third control current and each compensation circuit such that sum currents, flowing through the resistors and including half the second control current and the compensation currents, remain substantially constant when the value of the second control current changes.