AC coupling loops for current-to-voltage transimpedance amplifiers and methods of using same

A communication interface circuit for operating a plurality of interface protocols in response to communication signals, the communication signals being currents, the interface circuit converting the signal currents into signal voltages, the communication interface circuit comprising:

• a transimpedance circuit that receives the signal currents and converts the signal currents into signal voltages at an output terminal;
• a transconductance circuit that receives the signal voltages, the transconductance circuit comparing the signal voltages to a predetermined reference voltage and providing an output current in response to the comparison;
• a break frequency setting circuit for setting one break frequency selected from at least one available break frequency of the communication interface circuit, the setting circuit being coupled to the transconductance circuit to receive the output current;
• a correction current generation circuit coupled in series between the transconductance circuit and the transimpedance circuit, the generation circuit providing a correction current that forces the output of the transimpedance circuit to be substantially equal to the predetermined reference voltage at frequencies below the one break frequency;
• a first protocol interface circuit that receives the signal voltages, the first protocol interface circuit interpreting the signal voltages in accordance with a first protocol;
• and
• a second protocol interface circuit that receives the signal voltages, the second protocol interface circuit interpreting the signal voltages in accordance with a second protocol.

A transimpedance amplifier circuit including an AC coupling loop, the transimpedance amplifier circuit comprising:

• means for converting an input current to an output voltage at an output, the AC coupling loop including the means for converting;
• means for comparing the output voltage to a predetermined reference voltage and for generating a current in response to the comparison, the AC coupling loop including the means for comparing;
• means for setting one break frequency selected from at least one available break frequency of the transimpedance amplifier circuit coupled to a single interface point of the amplifier circuit at the output of the means for comparing;
• and
• means for producing a correction current at least in response to the current generated by the means for comparing, the AC coupling loop including the means for producing, the correction current forcing the output voltage from the means for converting to be substantially equal to the predetermined reference voltage at frequencies below the one break frequency.

A method for using a conversion circuit to convert a current to a voltage in response to input signals above one break frequency selected from at least one available break frequency, the method comprising the steps of:

• setting the one break frequency by changing circuitry coupled to a single interface point in the conversion circuit;
• inputting an input current having a given frequency;
• converting the input current to an output voltage;
• comparing the output voltage to a predetermined reference voltage;
• and
• producing a correction current if the given frequency is below the one break frequency, the correction current causing the step of converting to produce an output voltage substantially equal to the predetermined reference voltage.