Current source with active common mode rejection
A current source with active common mode rejection uses a principle of having a branch for the generation of the required current, to the output ( 107 ) of which one end of the load ( 3 ) is connected; and a branch of the active compensation circuit (ACC) ( 200 ), to the output ( 203 ) of which the other end of the load ( 3 ) is connected. By means of at least one input ( 201 ) of the ACC ( 200 ), at least one signal is sensed on the load, and subsequently it is processed so that the result of processing of at least one signal from at least one input ( 201 ) preferentially represents the common mode voltage, which corresponds to the pair of voltages at the voltage terminals ( 1 ) and ( 2 ) of the load ( 3 ), or voltage close to the common mode voltage. This result is subsequently processed by the regulating circuits of the ACC ( 200 ), which compare it to the reference potential value ( 4 ), and using the negative feedback principle, set such voltage on the output ( 203 ), which, within the control accuracy, leads to the equivalence of the reference potential ( 4 ) and the potential corresponding to the result of processing of at least one signal from at least one input ( 201 ).
1. A current source for connection with a load, the current source comprising:
a current control unit including feedback sensing inputs for sensing generated current by sensing voltage at a reference impedance or voltage at the load, and an output configured to be connected to the load; and
an active compensation circuit including a reference input configured to be connected to a reference node that is not connected to the load, and a compensation input configured to be connected to the load, and an output configured to be connected to the load such that the load is between the output of the current control unit and the output of the active compensation circuit,
the active compensation circuit further including a negative feedback circuit that is responsive to the reference input and the compensation input, to generate a signal on the output of the active compensation circuit,
wherein the negative feedback circuit is responsive to the compensation input via a signal that is a function of the compensation input, and
wherein the signal on the output of the active compensation circuit results in an equivalence of a signal applied to the reference input and the signal that is a function of the compensation input.
2. A current source according to claim 1 wherein the active compensation circuit has a regulating element for setting potential on the output of the active compensation circuit, the regulating element being of proportional-integral-derivative type or proportional-integral type, or of integral type.
3. A current source according to claim 2 wherein the active compensation circuit further includes a voltage follower or voltage amplifier to follow or amplify a signal from the compensation input.
4. A current source according to claim 3 wherein the regulating element includes a summing integrator.
5. A current source according to claim 1 wherein the active compensation circuit further includes an amplifier connected between the negative feedback circuit and the output of the active compensation circuit.
6. A current source according to claim 1 wherein the load includes a first end and a second end, the output of the current control unit is configured to be connected to the first end of the load, and the output of the active compensation circuit is configured to be connected to the second end of the load.
7. A current source according to claim 1 wherein the active compensation circuit further includes a second compensation input configured to be connected to the load such that the first and second compensation inputs measure a voltage drop on the load, and the negative feedback circuit is responsive to the reference input and a common mode voltage of the first and second compensation inputs, to generate the signal on the output of the active compensation circuit.
8. A current source according to claim 1 wherein the active compensation circuit further includes a second compensation input configured to be connected to the load such that the first and second compensation inputs measure a voltage drop on the load, and the negative feedback circuit is responsive to the reference input and a common mode voltage of the first and second compensation inputs, and wherein the signal on the output of the active compensation circuit results in an equivalence of a signal applied to the reference input and common mode voltage of the first and the second compensation inputs.