Patent ID: 6753738
Filing Date: 2004-06-22
Classification: H03B,H03J,H03L,H04L

Abstract:
A controlled resistance circuit forming a resistance between a first node and a second node having a controlled magnitude proportional to a reference resistance, said circuit comprising:a first variable resistance circuit connected between the first node and the second node, said first variable resistance circuit having an analog portion responsive to an analog control signal and having a digital portion responsive to a digital control signal, and whose magnitude is responsive to both the analog control signal and the digital control signal; a second variable resistance circuit connected between a third node and a fourth node, said second variable resistance circuit having an analog portion responsive to the analog control signal and having a digital portion responsive to the digital control signal, and whose magnitude, for a given value of the analog control signal and a given value of the digital control signal, is proportional to the magnitude of the first variable resistance circuit; a first feedback circuit responsive to a voltage developed across the second variable resistance circuit by a controlled first current flowing therethrough, for generating the analog control signal accordingly to adjust the magnitude of the second variable resistance circuit toward a magnitude which is proportional to the reference resistance; a second feedback circuit responsive to the analog control signal when the analog control signal is driven outside a predetermined range, for generating the digital control signal to accordingly further adjust the magnitude of the second variable resistance circuit in like direction as that resultant from the analog control signal being driven outside the predetermined range, so that the first feedback circuit drives the analog control signal back within the predetermined range; said first and second feedback circuits being arranged to generally maintain the analog control signal within the predetermined range and to adjust the magnitude of the second variable resistance circuit to a magnitude proportional to the reference resistance, thereby likewise adjusting the magnitude of the first variable resistance circuit to a controlled magnitude which is proportional to the reference resistance.