GMC filter and method for suppressing unwanted signals introduced by the filter

A GmC filter circuit comprising:

• a capacitor coupled in parallel to a current mode input;
• a differential emitter transistor circuit having first and second transistors wherein voltage across the capacitor is applied between base electrodes of the first and second, transistors, two emitter feedback resistors are coupled between emitter electrodes of the first and second transistors and two constant current sinks are coupled to the emitter electrodes of the first and second transistors;
• two diodes wherein the cathodes of the first and second diodes are coupled and the anode of the first diode is coupled to the collector of the first transistor and the anode of the second diode is coupled to the collector of the second transistor;
• a first emitter coupled transistor circuit having third and fourth transistors, wherein collector current of each of the first and second transistors is supplied to a base electrode of each of the third and fourth transistors, respectively, a constant current mode sink coupled to the emitters of the third and fourth transistors, and wherein collectors of the third and fourth transistors are coupled across the capacitor;
• and
• a second emitter coupled transistor circuit having fifth and sixth transistors, wherein collector current of each of the first and second transistors is supplied to a base electrode of each of the fifth and sixth transistors, respectively, a constant current mode sink coupled to the emitters of the fifth and sixth transistors, and wherein collectors of the fifth and sixth transistors supply a differential output in current mode.

A method for suppressing unwanted signals generated by a compression stage of a GmC filter, comprising the steps of:

• compressing an input signal using a first set of coefficients to produce a compressed signal;
• decompressing the compressed signal using a second set of coefficients to produce a decompressed signal at least a portion of which is fedback and combined with the input signal to suppress unwanted inband noise and DC offsets;
• and
• decompressing the compressed signal using a third set of coefficients to produce an output signal.

A GmC filter comprising:

• means for compressing an input signal using a first set of coefficients to produce a compressed signal;
• means for decompressing the compressed signal using a second set of coefficients to produce a decompressed signal at least a portion of which is fedback and combined with the input signal to suppress unwanted inband noise and DC offsets;
• and
• means for decompressing the compressed signal using a third set of coefficients to produce an output signal.