Fast settling current steering circuit
A selector switch may be controlled by a single-ended control signal for steering a current through a load or through an auxiliary line. The selector switch may include a first terminal to be coupled to the load, and a second terminal to be connected to the auxiliary line, and two analog switches coupled to respective ones of the first and second terminals and configured to implement a single pole double throw switch so that a conduction or non-conduction state is determined by the single-ended control signal for steering the current through the load or the auxiliary line. The selector switch may also include a circuit defining a positive feedback loop controlling the two analog switches.
1. A selector switch to be controlled by a single-ended control signal for steering a current through a load or through an auxiliary line, the selector switch comprising:
a first terminal to be coupled to the load, and a second terminal to be coupled to the auxiliary line;
respective analog switches coupled to said first and second terminals and configured to implement a single pole double throw switch so that a conduction state or a non-conduction state is determined by the single-ended control signal for steering the current through the load or the auxiliary line;
a differential output amplifier defining a positive feedback loop controlling said analog switches by amplifying a difference between the single-ended control signal and a voltage at said second terminal, and providing amplified differential voltages to said respective analog switches; and
a cascode stage generating the current as a function of an input single-ended signal.
2. The selector switch of claim 1 , wherein said analog switch coupled to said second terminal has a control node coupled to the single-ended control voltage; and wherein said circuit further comprises a differential amplifier having an output coupled to a control node of said analog switch coupled to said first terminal.
3. The selector switch of claim 1 wherein the auxiliary line comprises a dummy impedance coupled between said second terminal and a supply line.
4. The selector switch of claim 1 wherein said circuit comprises a control path for said analog switch coupled to said first terminal, said control path being coupled between a supply line and a common reference node.
5. The selector switch of claim 4 , wherein said control path comprises a transistor and an active load coupled in series therewith between the supply line and the common reference node; and wherein said analog switch coupled to said first terminal is controlled by a voltage on a common node between said active load and said transistor.
6. A selector switch to be controlled by a control signal for steering a current through a load or through an auxiliary line, the selector switch comprising:
a first terminal to be coupled to the load, and a second terminal to be coupled to the auxiliary line;
respective analog switches coupled to said first and second terminals and configured so that a conduction state or a non-conduction state is determined by the control signal for steering the current through the load or the auxiliary line;
a differential output amplifier controlling said analog switches by amplifying a difference between the control signal and a voltage at said second terminal, and providing amplified differential voltages to said respective analog switches; and
a cascode stage generating the current as a function of an input single-ended signal.
7. The selector switch of claim 6 , wherein the auxiliary line comprises a dummy impedance coupled between said second terminal and a supply line.
8. The selector switch of claim 6 wherein the control signal comprises a single-ended control signal.
9. The selector switch of claim 6 , wherein said analog switch coupled to said second terminal has a control node coupled to the control voltage; and wherein said circuit further comprises a differential amplifier having an output coupled to a control node of said analog switch coupled to said first terminal.
10. The selector switch of claim 6 , wherein said circuit comprises a control path for said analog switch coupled to said first terminal, said control path being coupled between a supply line and a common reference node.
11. A method for making a selector switch to be controlled by a control signal for steering a current through a load or through an auxiliary line, the method comprising:
providing a first terminal to be coupled to the load, and a second terminal to be coupled to the auxiliary line;
coupling respective analog switches to the first and second terminals and configured so that a conduction state or a non-conduction state is determined by the control signal for steering the current through the load or the auxiliary line;
coupling a differential output amplifier for a difference between the control signal and a voltage on the second terminal, and for generating amplified differential voltages to respective analog switches; and
coupling a cascode stage generating the current as a function of an input single-ended signal.
12. The method of claim 11 , wherein the control signal comprises a single-ended control signal.
13. The method of claim 11 wherein the analog switch coupled to the second terminal has a control node coupled to the control voltage; and wherein said circuit further comprises a differential amplifier having an output coupled to a control node of the analog switch coupled to the first terminal.