Output impedance control circuit

A method of controlling an output impedance of a circuit, the method comprising:

• generating first and second currents in response to voltages applied to an external resistance and to an internal resistance, said second current being proportional to the first current and being defined by a ratio of the external and internal resistances;
• generating third and fourth currents in response to the voltages applied to the external resistance and the internal resistance, said fourth current being proportional to the third current and being defined by the ratio of the external and internal resistances;
• generating a first control signal in response to the first and second currents;
• generating a second control signal in response to the third and fourth currents;
• and
• varying an output impedance of the circuit in response to the first and second control signals.

A digital camera comprising:

• a charge coupled device (CCD);
• a clock generator;
• a lens;
• and
• a CCD driver comprising:
• at least one resistive element;
• an output driver;
• and
• a first circuit adapted to generate a first control signal and a second control signal in response to a ratio of resistance of the at least one resistive element and a resistance of an external resistive element, said first and second control signals being adapted to cause an output impedance of the output driver to be substantially the same as or proportional to the resistance of the external resistive element.