Adjustable resistance device including first and second arrangements of a resistor and a positive-feedback transconductor, and a control circuit for controlling the resistances of the first and second arrangements

A resonance amplifier comprising:

• a first adjustable resistance device comprising a first arrangement of a first resistor and a first positive-feedback transconductor, said first arrangement having a control input;
• a second adjustable resistance device comprising a third arrangement of a third resistor and a third positive-feedback transconductor, said third arrangement having a control input;
• first and second capacitors, arranged in parallel with the first and the third arrangements;
• a fourth transconductor having an output coupled to the third arrangement and having an input coupled to the first arrangement;
• and
• a fifth transconductor having an output coupled to the input of the fourth transconductor and having an input coupled to the output of the fourth transconductor via a signal inverter, characterized in that the resonance amplifier further comprises a common control circuit having an output coupled to the control inputs of the first arrangement and the third parallel arrangement, the common control circuit comprising a control loop which includes:
• a second arrangement of a second resistor and a second positive-feedback transconductor, said second arrangement being arranged between a first node and a second node, and having a control input;
• a sixth transconductor having an output coupled to a supply line and having an input arranged in parallel with the input of the second positive-feedback transconductor;
• a comparator circuit having a first and a second input coupled to the first node and the second node, respectively, and having an output which forms the output of the common control circuit and which is also coupled to the control input of the second arrangement,
• the second parallel arrangement differing from the first arrangement and the third arrangement in that the first resistor and the third resistor are smaller in value than the second resistor.

A receiver successively comprising a selectivity stage, a demodulation device and an LF section, characterized in that the selectivity stage comprises a resonance amplifier comprising:

• a first adjustable resistance device comprising a first arrangement of a first resistor and a first positive-feedback transconductor, said first arrangement having a control input;
• a second adjustable resistance device comprising a third arrangement of a third resistor and a third positive-feedback transconductor, said third arrangement having a control input;
• first and second capacitors, arranged in parallel with the first and the third arrangements;
• a fourth transconductor having an output coupled to the third arrangement and having an input coupled to the first arrangement;
• and
• a fifth transconductor having an output coupled to the input of the fourth transconductor and having an input coupled to the output of the fourth transconductor via a signal inverter, wherein the resonance amplifier further comprises a common control circuit having an output coupled to the control inputs of the first arrangement and the third parallel arrangement, the common control circuit comprising a control loop which includes:
• a second arrangement of a second resistor and a second positive-feedback transconductor, said second arrangement being arranged between a first node and a second node, and having a control input;
• a sixth transconductor having an output coupled to a supply line and having an input arranged in parallel with the input of the second positive-feedback transconductor;
• a comparator circuit having a first and a second input coupled to the first node and the second node, respectively, and having an output which forms the output of the common control circuit and which is also coupled to the control input of the second arrangement, the second parallel arrangement differing from the first arrangement and the third arrangement in that the first resistor and the third resistor are smaller in value than the second resistor.

A resonance amplifier comprising:

• a first adjustable resistance device comprising a first arrangement of a first resistor and a first positive-feedback transconductor, said first arrangement having a control input;
• a second adjustable resistance device comprising a third arrangement of a third resistor and a third positive-feedback transconductor, said third arrangement having a control input;
• first and second capacitors, arranged in parallel with the first and the third arrangements;
• a fourth transconductor having an output coupled to the third arrangement and having an input coupled to the first arrangement;
• and
• a fifth transconductor having an output coupled to the input of the fourth transconductor and having an input coupled to the output of the fourth transconductor via a signal inverter, characterized in that the resonance amplifier further comprises a common control circuit having an output coupled to the control inputs of the first arrangement and the third parallel arrangement, the common control circuit comprising a control loop which includes:
• a second arrangement of a second resistor and a second positive-feedback transconductor, said second arrangement being arranged between a first node and a second node, and having a control input;
• a sixth transconductor having an output coupled to a supply line and having an input arranged in parallel with the input of the second positive-feedback transconductor;
• a comparator circuit having a first and a second input coupled to the first node and the second node, respectively, and having an output which forms the output of the common control circuit and which is also coupled to the control input of the second arrangement, the second parallel arrangement differing from the first arrangement and the third arrangement in that the transconductances of the first transconductor and the third transconductor are smaller than the transconductance of the second transconductor.

A receiver successively comprising a selectivity stage, a demodulation device and an LF section, characterized in that the selectivity stage comprises a resonance amplifier comprising:

• a first adjustable resistance device comprising a first arrangement of a first resistor and a first positive-feedback transconductor, said first arrangement having a control input;
• a second adjustable resistance device comprising a third arrangement of a third resistor and a third positive-feedback transconductor, said third arrangement having a control input;
• first and second capacitors, arranged in parallel with the first and the third arrangements;
• a fourth transconductor having an output coupled to the third arrangement and having an input coupled to the first arrangement;
• and
• a fifth transconductor having an output coupled to the input of the fourth transconductor and having an input coupled to the output of the fourth transconductor via a signal inverter, wherein the resonance amplifier further comprises a common control circuit having an output coupled to the control inputs of the first arrangement and the third parallel arrangement, the common control circuit comprising a control loop which includes:
• a second arrangement of a second resistor and a second positive-feedback transconductor, said second arrangement being arranged between a first node and a second node, and having a control input;
• a sixth transconductor having an output coupled to a supply line and having an input arranged in parallel with the input of the second positive-feedback transconductor;
• a comparator circuit having a first and a second input coupled to the first node and the second node, respectively, and having an output which forms the output of the common control circuit and which is also coupled to the control input of the second arrangement, the second parallel arrangement differing from the first arrangement and the third arrangement in that the transconductances of the first transconductor and the third transconductor are smaller than the transconductance of the second transconductor.