Accurate radio frequency filtering using active intermediate frequency feedback

A system comprising a radio frequency (RF) filter circuit comprising:

• a filter;
• a first node;
• a second node coupled to the filter;
• a conversion signal path having an input coupled to the first node and an output coupled to the second node the conversion signal path comprising an active mixer coupled between the first node and the second node;
• a feedback signal path having an input coupled to the second node and an output coupled to the first node the feedback signal path comprising a first transconductor and a first mixer coupled in series between the second node and the first node;
• wherein the active mixer comprises a second transconductor and a second mixer coupled in series between the first node and the second node;
• and
• wherein:
• the second transconductor comprises an input coupled to the first node and an output;
• the second mixer comprises a first input coupled to the output of the second transconductor, a second input to receive a reference signal, and an output coupled to the second node;
• the first transconductor comprises an input coupled to the second node and an output;
• and
• the first mixer comprises a first input coupled to the output of the first transconductor, a second input to receive a reference signal, and an output coupled to the first node.

A system comprising:

• a radio frequency (RF) filter circuit comprising:
• a filter coupled between a first node and a second node;
• a primary conversion signal path having an input coupled to a third node and an output coupled to the first node, the primary conversion signal path comprising a first transconductor and a first mixer coupled in series between the third node and the first node, the first mixer to receive a first reference signal having a first frequency fLO;
• a first harmonic feedforward signal path having an input coupled to the third node and an output coupled to the first node, the first harmonic feedforward signal path having a second transconductor and a second mixer coupled in series between the third node and the first node, the second mixer to receive a second reference signal having a frequency n*fLO, wherein n is a positive odd integer;
• a feedback signal path having an input coupled to the second node and an output coupled to the third node, the feedback signal path comprising a third transconductor and a third mixer coupled in series between the second node and the third node, the third mixer to receive the first reference signal;
• and
• a second harmonic feedforward signal path having an input coupled to the second node and an output coupled to the third node, the second harmonic feedforward signal path having a fourth transconductor and a fourth mixer coupled in series between the second node and the third node, the fourth mixer to receive the second reference signal.