Wideband monolithic tunable high-Q notch filter for image rejection in RF application

A wideband tunable high Q image rejection notch filter comprising:

• a Q-enhancement circuit used in a notch filter by creating a negative resistance to compensate for resistive losses in inductive components of said Q-enhancement circuit, said Q-enhancement circuit comprising:
• a differential series LC resonator comprising a first and a second transistor, where the source and the drain of said first and said second transistor are paralleled by a first and a second capacitive means, respectively, where a first and a second inductive means is coupled across the gate and the drain of said first and said second transistor, respectively, where the drains of said first and said second transistor are the input terminals of said Q-enhancement circuit, where the sources of said first and said second transistor are coupled together via capacitance means, where the source and gate of said first transistor is coupled via first and second terminals of a first capacitance tunable varactor means, where the source and gate of said second transistor is coupled via first and second terminals of a second capacitance tunable varactor means, and where a third terminal of said first and said second capacitance tunable varactor means is coupled to an input port providing an input signal, said varactors extending the notch frequency band of said Q-enhancement circuit, and where said differential series LC resonator is a transconductor based negative resistance generator resonating at the image frequency to compensate for the resistance of said inductive means;
• a differential Q compensation circuit providing extra negative impedance to further compensate for the resistance of said inductive means of said differential series LC resonator, said differential Q compensation circuit comprising a cross-coupled differential third and fourth transistor, the drain of said third and fourth transistor coupled to the source of said first and said second transistor, respectively, and
• a current source coupled between a reference voltage and the source of said third and said fourth transistor, said current source providing a bias current for said Q-enhancement circuit.

A wideband tunable high Q image rejection notch filter comprising:

• a first cascoded LNA having an input and an output, said first cascoded LNA receiving an RF input signal at said input and providing at its output an amplified signal of said RF input signal;
• a second cascoded LNA having an input and an output, said second cascoded LNA input coupled to said output of said first LNA, said second LNA rejecting on-chip common-mode noise;
• a Q-enhancement circuit coupled to said second cascoded LNA, said Q-enhancement circuit used in a notch filter by creating a negative resistance to compensate for resistive losses in inductive components of said Q-enhancement circuit, said Q-enhancement circuit comprising:
• a differential series LC resonator comprising a first and a second transistor, where the source and the drain of said first and said second transistor are paralleled by a first and a second capacitive means, respectively, where a first and a second inductive means is coupled across the gate and the drain of said first and said second transistor, respectively, where the drains of said first and said second transistor are coupled to said second cascoded LNA, where the sources of said first and said second transistor are coupled together via a first and a second terminal of a capacitance tunable varactor means, where a third terminal of said capacitance tunable varactor means is coupled to a third port providing an input signal, and where the drain of said first and said second transistor is coupled via capacitive means to the gate of said first and said second transistor, respectively, where said differential series LC resonator is a transconductor based negative resistance generator resonating at the image frequency to compensate for the resistance of said inductive means;
• a differential Q compensation circuit providing extra negative impedance to further compensate for the resistance of said inductive means of said differential series LC resonator, said differential Q compensation circuit comprising a cross-coupled differential third and fourth transistor, the drain of said third and fourth transistor coupled to the source of said first and said second transistor, respectively, and
• a tunable current source coupled between said third port and the source of said third and said fourth transistor, said tunable current source comprising an analog multiplier, two voltage controlled current sources and a fixed current source, said tunable current source improving the image rejection of said notch filter in a wide frequency band by providing for said Q-enhancement circuit a bias current which is the quadratic function of the tuning voltage across said tunable varactor means.

A wideband tunable high Q image rejection notch filter comprising:

• a first cascoded LNA having an input and an output, said first cascoded LNA receiving an RF input signal at said input and providing at its output an amplified signal of said RF input signal;
• a second cascoded LNA having an input and an output, said second cascoded LNA input coupled to said output of said first LNA, said second LNA rejecting on-chip common-mode noise;
• a Q-enhancement circuit coupled to said second cascoded LNA, said Q-enhancement circuit used in a notch filter by creating a negative resistance to compensate for resistive losses in inductive components of said Q-enhancement circuit, said Q-enhancement circuit comprising:
• a differential series LC resonator comprising a first and a second transistor, where the source and the drain of said first and said second transistor are paralleled by a first and a second capacitive means, respectively, where a first and a second inductive means is coupled across the gate and the drain of said first and said second transistor, respectively, where the drains of said first and said second transistor are coupled to said second cascoded LNA, where the sources of said first and said second transistor are coupled together via capacitance means, where the source and gate of said first transistor is coupled via first and second terminals of a first capacitance tunable varactor means, where the source and gate of said second transistor is coupled via first and second terminals of a second capacitance tunable varactor means, and where a third terminal of said first and said second capacitance tunable varactor means is coupled to a third port providing an input signal, said varactors extending the notch frequency band of said Q-enhancement circuit, and where said differential series LC resonator is a transconductor based negative resistance generator resonating at the image frequency to compensate for the resistance of said inductive means;
• a differential Q compensation circuit providing extra negative impedance to further compensate for the resistance of said inductive means of said differential series LC resonator, said differential Q compensation circuit comprising a cross-coupled differential third and fourth transistor, the drain of said third and fourth transistor coupled to the source of said first and said second transistor, respectively, and
• a current source coupled between a reference voltage and the source of said third and said fourth transistor, said current source providing a bias current for said Q-enhancement circuit.

A wideband tunable high Q image rejection notch filter comprising:

• a single ended cascoded LNA having an input and a single output, said single ended cascoded LNA receiving an RF input signal at said single input and providing at said single output an amplified signal of said RF input signal;
• a differential cascoded LNA having a single input and a differential output, said single input of said differential cascoded LNA coupled to said single output of said single ended cascoded LNA, said differential cascoded LNA rejecting on-chip common-mode noise;
• a Q-enhancement circuit coupled to said differential cascoded LNA, said Q-enhancement circuit used in a notch filter by creating a negative resistance to compensate for resistive losses in inductive components of said Q-enhancement circuit, said Q-enhancement circuit comprising:
• a differential series LC resonator comprising a first and a second transistor, where the source and the drain of said first and said second transistor are paralleled by a first and a second capacitive means, respectively, where a first and a second inductive means is coupled across the gate and the drain of said first and said second transistor, respectively, where the drains of said first and said second transistor are coupled to said second cascoded LNA, where the sources of said first and said second transistor are coupled together via a first and a second terminal of a capacitance tunable varactor means, where a third terminal of said capacitance tunable varactor means is coupled to a reference potential, and where the drain of said first and said second transistor is coupled via capacitive means to the gate of said first and said second transistor, respectively, where said differential series LC resonator is a transconductor based negative resistance generator resonating at the image frequency to compensate for the resistance of said inductive means;
• a differential Q compensation circuit providing extra negative impedance to further compensate for the resistance of said inductive means of said differential series LC resonator, said differential Q compensation circuit comprising a cross-coupled differential third and fourth transistor, the drain of said third and fourth transistor coupled to the source of said first and said second transistor, respectively, and
• a current source coupled between said reference voltage and the source of said third and said fourth transistor, said current source providing a bias current for said Q-enhancement circuit.