Apparatus and method for producing a temperature-independent current signal in an automatic gain control circuit

An integrated circuit for the generation of a direct current for control of the gain of an amplifier as a function of the difference between a reference voltage and a signal voltage proportional to the amplitude of the output signal from said amplifier, which comprises:

• first means able to drive a bias current directly proportional to temperature and inversely proportional to the value of at least a first integrated resistor comprised therein;
• a first differential stage driven by said bias current and having a first input and a second input and a first and a second output, which is able to carry out a voltage/voltage conversion, in accordance with an exponential law, of a differential input voltage applied to said inputs;
• a current generator able to drive a constant bias current essentially independent of temperature variations;
• a second differential stage driven by said constant bias current and having a first input connected to said first output of said first differential stage and a second input connected to said second output of said first differential stage and which is able to carry out a voltage/current conversion, in accordance with an exponential law, in order to generate said output current at an output terminal, as a function of the differential voltage applied to said inputs;
• and
• a differential input circuit having a first input terminal to which is applied said signal voltage and a second input terminal to which is applied said reference voltage, essentially independent of temperature, and formed by a pair of transistors connected in a common-emitter configuration, respectively biased by means of two identical generators of current respectively connected between a first supply node of the circuit and the emitters of said transistors and which are able to generate a current inversely proportional to the value of at least a second integrated resistor, which emitters are interconnected across said second integrated resistor, and which transistors have identical, forward-biased diodes as respective loads, respectively connected between the collectors of said transistors and a second supply node for a virtual supply node of the circuit, the differential output voltage across the collector nodes of said pair of transistors representing a current/voltage conversion provided by said forward-biased diodes, in accordance with a logarithmic law, of the respective currents flowing through the transistors of said pair and being applied to the inputs of said first differential stage, which currents represent a voltage/current conversion, in accordance with a linear/logarithmic law of the difference between said signal voltage and said reference voltage.

An integrated circuit for the generation of a current independent of temperature and proportional to the difference between a signal voltage and a reference voltage, which comprises:

• a first and second current generators, each of said current generators generating the same current, I.sub.G, the value of which is inversely proportional to the value of at least a first integrated resistor electrically coupled to said first and second current generators;
• a differential input circuit having a first and second branches, said first branch coupled to and biased by said first current generator and having a first input that is connected to the signal voltage, said second branch coupled to and biased by said second current generator and having a second input that is connected to the reference voltage, said first and second branches generating a first and second output currents proportional to the difference between the signal voltage and the reference voltage;
• a load circuit, electrically connected to said differential input circuit, to provide an electrical load to said differential input circuit to perform a linear to logarithmic conversion of said first and second output currents and generate a differential voltage signal proportional to temperature and said first and second output currents from said differential input circuit:
• a bias current circuit to generate a bias current proportional to variations in temperature and inversely proportional to the value of at least a second integrated resistor comprised therein;
• a voltage conversion circuit that generates a converted voltage, the voltage conversion circuit being electrically connected to said bias current circuit and said load circuit, driven by said bias current from said bias current circuit and receiving said differential voltage signal from said load circuit, said voltage conversion circuit performing a voltage/voltage conversion of said differential voltage signal according to an exponential law to generate said converted voltage;
• and
• an output circuit, electrically connected to said voltage conversion circuit, to receive said converted voltage and convert said converted voltage into a temperature-independent output current whose current value is proportional to the difference between said first input and said second input and is independent of temperature variations.

An integrated circuit for the generation of a temperature independent direct current for the control of the gain of an amplifier as a function of the difference between a reference proportional to the amplitude of the output signal from said amplifier, said integrated circuit comprising:

• first and second current generators, each of said current generators generating the same current, I.sub.G, the value of which is temperature dependent;
• a differential input circuit having a first and second branches, said first branch including a first transistor coupled to and biased by said first current generator, and having a first input that is connected to the signal voltage, said second branch including a second transistor coupled to and biased by said second current generator and having a second input that is connected to the reference voltage, said first and second branches generating a first and second output currents proportional to the difference between the signal voltage and the reference voltage;
• a load circuit, electrically connected to said differential input circuit, to provide an electrical load to said differential input circuit, said load circuit comprising a first and second diode and a voltage-dropping resistor, said resistor connected between a power supply and the anodes of both said first and second diodes to provide a voltage drop, the cathode of said first diode being connected to the collector of said first transistor the cathode of said second diode being connected to the collector of said second transistor, the output of said load circuit being a first and second signals forming a differential voltage signal proportional to temperature and said first and second output currents from said differential input circuit:
• a bias current circuit to generate a bias current proportional to variations in temperature and inversely proportional to the value of at least a first integrated resistor comprised therein;
• a voltage conversion circuit that generates a converted voltage, the voltage conversion circuit being electrically connected to said bias current circuit and said load circuit, driven by said bias current from said bias current and receiving said differential voltage signal from said load circuit, said voltage conversion circuit performing a voltage/voltage conversion of said differential voltage signal to generate said converted voltage;
• and
• an output circuit, electrically connected to said voltage conversion circuit, to receive said converted voltage and convert said converted voltage into a temperature-independent output current whose current value is proportional to the difference between said first input and said second input and is independent of temperature variations.