Current steering for high-frequency pixel modulation
A current-load control circuit can include a first and second current loads, a current source, and a current-steering switch. The current-steering switch is operable to connect the first current load to the current source in a first switch mode to direct electrical current from the current source through the first current load and is operable to connect the second current load to the current source in a second switch mode different from the first switch mode to direct electrical current from the current source through the second current load. The first current load can be a light emitter. The second current load can be a light emitter or a non-emissive current load. A display can include an array of current-load control circuits. A digital camera can record images shown on the display to communicate information from the display to the digital camera.
1 . A current-steering circuit, comprising:
a first current load that is a light emitter;
a second current load;
a current source or current sink; and
a current-steering switch,
wherein the current-steering switch is operable to connect the first current load to the current source or current sink in a first switch mode and is operable to connect the second current load to the current source or current sink in a second switch mode different from the first switch mode, and
wherein the current source or current sink is a current source and the current-steering switch is operable to switch current from the current source at a frequency no less than 1 MHz
the current source or current sink is a current sink and the current-steering switch is operable to switch current to the current sink at a frequency no less than 1 MHz.
2 . The current-steering circuit of claim 1 , wherein the second current load is a non-light-emissive load.
3 . The current-steering circuit of claim 1 , wherein the light emitter is a first light emitter and the second current load is a second light emitter.
4 . The current-steering circuit of claim 3 , wherein the second light emitter emits light that has a different frequency from light emitted by the first light emitter.
5 . The current-steering circuit of claim 4 , wherein the second light emitter emits light that is not visible to a human visual system.
6 . The current-steering circuit of claim 1 , wherein the current source or current sink is a constant-current source or constant-current sink.
7 . The current-steering circuit of claim 1 , wherein the current source or current sink is constructed such that current provided thereby is a current selected to optimize efficiency of light emission from the light emitter.
8 . The current-steering circuit of claim 1 , wherein the current-steering switch comprises a current-steering transistor connected to each current load to control flow of current through the current load, the current-steering transistor responsive to a switch-control signal.
9 . The current-steering circuit of claim 1 , wherein the current-steering switch comprises a differential pair of transistors comprising sources and drains, wherein (i) the sources are connected in common to form a common connection and the drains form separate connections or (ii) the drains form a common connection and the sources form separate connections, wherein one of the differential pair of transistors is responsive to a positive switch-control signal and another of the differential pair of transistors is responsive to a negative version of the positive switch-control signal.
10 . The current-steering display of claim 1 , comprising a plurality of the current-steering circuits, wherein the current-steering display is a high-frame-rate display having a frame rate no less than 600 Hz.
11 . A current-steering circuit, comprising:
a first current load that is a light emitter;
a second current load;
a current source or current sink; and
a current-steering switch,
wherein the current-steering switch is operable to connect the first current load to the current source or current sink in a first switch mode and is operable to connect the second current load to the current source or current sink in a second switch mode different from the first switch mode, and
wherein the current-steering switch is responsive to a multi-bit switch-control signal comprising control bits, wherein the current-steering switch comprises successive levels of differential pairs of transistors, each successive level controlled by a different one of the control bits to provide the switch-control signal, wherein a final level of the successive levels controls current flow through the first current load and the second current load.
12 . The current-steering circuit of claim 11 , wherein each of the differential pair of transistors comprises sources and drains, wherein (i) the sources are connected in common to form a common connection and the drains form separate connections or (ii) the drains form a common connection and the sources form separate connections.
13 . The current-steering circuit of claim 11 , wherein the second current load is a non-light-emissive load.
14 . The current-steering circuit of claim 11 , wherein the light emitter is a first light emitter and the second current load is a second light emitter.
15 . The current-steering circuit of claim 14 , wherein the second light emitter emits light that has a different frequency from light emitted by the first light emitter.
16 . The current-steering circuit of claim 15 , wherein the second light emitter emits light that is not visible to a human visual system.
17 . The current-steering circuit of claim 11 , wherein the current source or current sink is a constant-current source or constant-current sink.
18 . The current-steering circuit of claim 11 , wherein the current source or current sink is constructed such that current provided thereby is a current selected to optimize efficiency of light emission from the light emitter.
19 . The current-steering circuit of claim 11 , wherein the current-steering switch comprises a current-steering transistor connected to each current load to control flow of current through the current load, the current-steering transistor responsive to a switch-control signal.
20 . The current-steering circuit of claim 11 , wherein the current-steering switch comprises a differential pair of transistors comprising sources and drains, wherein (i) the sources are connected in common to form a common connection and the drains form separate connections or (ii) the drains form a common connection and the sources form separate connections, wherein one of the differential pair of transistors is responsive to a positive switch-control signal and another of the differential pair of transistors is responsive to a negative version of the positive switch-control signal.
21 . The current-steering display of claim 11 , comprising a plurality of the current-steering circuits, wherein the current-steering display is a high-frame-rate display having a frame rate no less than 600 Hz.