Radiofrequency detector circuit and corresponding radiofrequency detection method

1 . A radiofrequency detector comprising:

a squarer circuit comprising:

a first branch coupled between a voltage supply and ground, the first branch comprising a first squarer transistor configured to receive a radiofrequency sinusoidal input voltage, wherein the first squarer transistor is coupled to the voltage supply through a first load; and

a second branch coupled between the voltage supply and the ground, the second branch comprising a second reference transistor coupled to the voltage supply through a second load, wherein an output voltage is formed at an output node of the first branch and a reference voltage is formed at a respective output node coupled to the second load of the second branch, and wherein a squared voltage is obtained by a difference voltage of the output voltage and the reference voltage;

wherein the squarer circuit is configured to feed back to a control electrode of the second reference transistor a feedback signal that is a function of the difference voltage.

2 . The radiofrequency detector of claim 1 , wherein the squarer circuit comprises a sense amplifier having inputs coupled to the output voltage and the reference voltage, wherein the sense amplifier is configured to output a signal proportional to the difference voltage of the output voltage and the reference voltage, to the control electrode of the second reference transistor.

3 . The radiofrequency detector of claim 2 , wherein the squarer circuit comprises a cascode transistor on each of the first branch and the second branch, arranged between the first squarer transistor or the second reference transistor, respectively, and a current steering circuit injecting current in the respective node in common between the first squarer transistor or the second reference transistor, respectively, and the respective cascode transistor.

4 . The radiofrequency detector of claim 1 , wherein the control electrode of the second reference transistor is a gate of the second reference transistor.

5 . The radiofrequency detector of claim 1 , wherein the control electrode of the second reference transistor is a bulk electrode gate of the second reference transistor.

6 . The radiofrequency detector of claim 2 , further comprising a low pass filter configured to receive the output voltage and the reference voltage, and output corresponding low pass filtered signals to the inputs of the sense amplifier.

7 . The radiofrequency detector of claim 1 , wherein the squarer circuit is single ended.

8 . The radiofrequency detector of claim 1 , wherein the squarer circuit is differential and comprises two squarer transistors in parallel configured to receive as input positive and negative RF input signals.

9 . The radiofrequency detector of claim 1 , wherein the first squarer transistor and the second reference transistor are metal-oxide-semiconductor field-effect transistors (MOSFETs).

10 . The radiofrequency detector of claim 1 , further comprising an envelope detector coupled to at least the first branch, wherein the envelope detector comprises a first p-channel MOS (pMOS) transistor coupled by its gate to the output voltage and having an output through a respective capacitor to a voltage supply node or to a ground reference node.

11 . The radiofrequency detector of claim 10 , wherein the envelope detector further comprises a second pMOS transistor coupled by its gate to the reference voltage and having an output coupled to the voltage supply by a further respective capacitor, and wherein the outputs of the first and second pMOS transistors are coupled to respective buffers.

12 . The radiofrequency detector of claim 10 , wherein the envelope detector is configured to apply a respective detector refence voltage to the gate of the first pMOS transistor, wherein the respective capacitor is coupled to the ground and to a first input of a differential amplifier having an output coupled to a gate of a second pMOS transistor having an output coupled back to a second input of the differential amplifier.

13 . The radiofrequency detector of claim 10 , wherein a source of the first pMOS transistor is coupled to the voltage supply through a decay current generator configured to inject a decay current in the source of the first pMOS transistor.

14 . The radiofrequency detector of claim 11 , wherein the output of the buffer coupled to the second pMOS transistor, or the output of the second pMOS transistor, is coupled to an analog to digital converter.

15 . A method of operating a radiofrequency detector, the radiofrequency detector comprising a squarer circuit comprising first and second branches coupled between a voltage supply and ground, the first branch comprising a first squarer transistor coupled to the voltage supply through a first load, the second branch comprising a second reference transistor coupled to the voltage supply through a second load, the method comprising:

receiving, by the first squarer transistor, a radiofrequency sinusoidal input voltage;

generating an output voltage at an output node of the first branch;

generating a reference voltage at a respective output node coupled to the second load of the second branch;

obtaining a squared voltage from a difference voltage of the output voltage and the reference voltage; and

feeding back to a control electrode of the second reference transistor a feedback signal that is a function of the difference voltage.

16 . The method of claim 15 , wherein the squarer circuit comprises a sense amplifier having inputs coupled to the output voltage and the reference voltage, and the method further comprises:

outputting, by the sense amplifier, a signal proportional to the difference voltage of the output voltage and the reference voltage, to the control electrode of the second reference transistor.

17 . The method of claim 16 , wherein the squarer circuit comprises a cascode transistor on each of the first branch and the second branch, arranged between the first squarer transistor or the second reference transistor, respectively, and the method further comprises:

injecting, by a current steering circuit, current in the respective node in common between the first squarer transistor or the second reference transistor, respectively, and the respective cascode transistor.

18 . The method of claim 16 , further comprising:

receiving, by a low pass filter, the output voltage and the reference voltage; and

outputting, by the low pass filter, corresponding low pass filtered signals to the inputs of the sense amplifier.

19 . The method of claim 15 , wherein the radiofrequency detector further comprises an envelope detector comprising a first p-channel MOS (pMOS) transistor coupled by its gate to the output voltage, and a second pMOS transistor coupled by its gate to the reference voltage, and the method further comprises:

using, by the envelope detector, the reference voltage to remove a direct current offset from the squarer circuit.

20 . The method of claim 15 , wherein the radiofrequency detector further comprises an envelope detector comprising a first p-channel MOS (pMOS) transistor coupled by its gate to the output voltage, an operational amplifier having a first input coupled to an output of the first pMOS transistor and a second input coupled to an output of a second pMOS transistor, and the second pMOS transistor, coupled by its gate to an output of the operational amplifier, and the method further comprises:

receiving, at the gate of the first pMOS transistor, a detector reference voltage; and

using, by the envelope detector, the detector reference voltage to direct current bias the envelope detector.