Patent ID: 7227412

Claim:
An attenuation cell having an attenuation factor control device with first and second input electrodes and first and second output electrodes, the attenuation cell comprising: a first differential pair having a first bipolar transistor and a second bipolar transistor, said first and second transistors each having a transmitter electrode connected to a first power source and to said first input electrode, said first transistor having a collector connected to said first output electrode; a second differential pair having a third bipolar transistor and a fourth bipolar transistor, said third and fourth bipolar transistors each having a transmitter electrode connected to a second power source and to said second input electrode, said fourth transistor having a collector connected to said second output electrode; said first and fourth bipolar transistors having a base that is connected to a same voltage VA and said second and third bipolar transistors having a base connected to a same voltage VB; and an attenuation factor control circuit for setting voltages VA and VB respectively, including: a first diode seeing a current IA so as to generate a voltage difference controlling said voltage VA; a second diode seeing a current IB so as to generate a voltage difference controlling said voltage VB; a third diode seeing a sum IA+IB of the currents flowing through said first and second diodes, said sum being generated by a third power source so as to generate a voltage difference VC corresponding to the sum of currents IA+IB; an amplifier having two inputs connected to receive voltages VB and VC generated by said second and said third diode respectively, said amplifier generating information Iz representative of a difference between the voltages VB and VC; a converter circuit receiving a desired value Vet varying linearly and generating a first value Ix; a multiplier circuit receiving said first intermediate value and generating a second value Iy proportional to said desired voltage Vct and to an absolute temperature T; and an error amplifier receiving error Iy−Iz as an input and generating currents IA and IB in order to minimize said error.