Claims
- 1. An apparatus comprising:
a current source; a scaling circuit coupled to said current source to control a value of current from said current source; and a switch coupled to said current source to switch said current on to a load, said switch being responsive to an input signal operating at one supply voltage, but in which the value of current through the load provides an output signal compatible to operate at a second supply voltage.
- 2. The apparatus of claim 1 wherein the second supply voltage is lower in value than the first supply voltage.
- 3. The apparatus of claim 2 wherein the input signal is a clocking signal received from a clocking device operating at the first supply voltage and the output signal is the clocking signal reduced in voltage to clock circuitry operating at a lower supply voltage than the clocking device.
- 4. The apparatus of claim 1 wherein said current source provides a high impedance drive to the load at an operating range which maintains the current substantially constant, even if variations of the first supply voltage occurs.
- 5. The apparatus of claim 1 wherein said current source provides a high impedance drive to the load to provide noise rejection to maintain a substantially constant current over a specified voltage swing of the output signal.
- 6. The apparatus of claim 1 where in said current source includes a current mirror coupled to said scaling circuit, in which said scaling circuit develops a voltage across an impedance to determine a reference current for said current mirror, the reference current used to establish a mirror current for said current mirror and the mirror current is then switched to the load.
- 7. The apparatus of claim 6 wherein said scaling circuit uses a voltage reference to establish scaling of an input signal voltage swing to an output signal voltage swing to make the output signal compatible to operate at the second supply voltage.
- 8. The apparatus of claim 1 wherein said switch operates at a higher of the two supply voltages and isolates the lesser supply voltage from the higher supply voltage.
- 9. A driver circuit comprising:
a first transistor and a second transistor coupled in parallel to provide a differential output signal, said first and second transistors having their gates coupled to receive a differential input signal and in which said first and second transistors operate as a switch to have a voltage swing of the input signal reduced in amplitude to generate the output signal having less of a voltage swing than the input signal; a third transistor and a fourth transistor arranged to form a current mirror to provide a reference current and a mirror current respectively, said fourth transistor coupled to said first and second transistors, in which the mirror current when coupled to a load generates the differential output signal; and a voltage scaling circuit coupled to said current mirror to establish a scaling voltage to establish scaling of signal reduction between the input signal and the output signal, the scaling voltage when coupled to a reference impedance establishes a value for the reference current.
- 10. The driver circuit of claim 9 wherein the input signal operates at a first supply voltage and the output signal is at second supply voltage which is lower than the first supply voltage.
- 11. The driver circuit of claim 10 wherein the input signal is a clocking signal received from a clocking device operating at the first supply voltage and the output signal is the clocking signal reduced in voltage to clock circuitry operating at a lower supply voltage than the clocking device.
- 12. The driver circuit of claim 11 wherein said first, second and fourth transistors present a sufficiently high impedance to maintain a substantially constant current over a range of voltages available for the output signal.
- 13. The driver circuit of claim 10 wherein said first, second and fourth transistors provide a sufficiently high impedance drive to a load at an operating range which maintains the mirror current substantially constant, even if variations of the first supply voltage occurs.
- 14. The driver circuit of claim 13 wherein said first and second transistors isolate the first supply voltage from the second supply voltage.
- 15. The driver circuit of claim 14 further including a plurality of transistors arranged in parallel to said fourth transistor to form a number of branches, wherein each branch is to be switched in to change the mirror current for a given reference current to change the voltage swing of the output signal.
- 16. A method comprising:
providing a substantially constant output current to a load to develop a voltage across the load as an output signal, the output current under control of a switch controlled by an input signal; scaling the output current to develop the voltage across the load so that the output signal follows the input signal, but having less of a voltage swing to scale the output signal to the input signal at a predetermined ratio; and driving the load at sufficiently high impedance to maintain a substantially constant current over the range of voltage developed by the load.
- 17. The method of claim 16 wherein the input signal operates at a first supply voltage and the output signal is used to drive a circuit having a second supply voltage which is lower than the first.
- 18. The method of claim 17 wherein the input signal is a clocking signal received from a clocking circuit operating at the first supply voltage and the output signal is the clocking signal reduced in voltage to clock circuitry operating at the lower second supply voltage.
- 19. A system comprising:
a signal generation device operating at a first supply voltage; a processor operating at a second supply voltage; a signal level transitioning circuit coupled to said processor and said signal generation device to transition a signal from said signal generation device which is operating at the first supply voltage to be compatible with said processor operating at the second supply voltage which is less in magnitude than the first supply voltage, said signal transitioning level circuit comprising:
(a) a current source; (b) a scaling circuit coupled to said current source to control a value of current from said current source; and (c) a switch coupled to said current source to switch said current on to a load, said switch being responsive to the input signal and in which the value of current through the load provides the output signal compatible to operate at the second supply voltage.
- 20. The system of claim 19 wherein said current source provides a high impedance drive to the load at an operating range which maintains the current substantially constant, even if variations of the first supply voltage occurs.
- 21. The system of claim 19 wherein said current source provides a high impedance drive to the load to provide noise rejection to maintain a substantially constant current over a specified voltage swing of the output signal.
- 22. The system of claim 19 where in said current source includes a current mirror coupled to said scaling circuit, in which said scaling circuit develops a voltage across an impedance to determine a reference current for said current mirror, the reference current used to establish a mirror current for said current mirror and the mirror current is then switched to the load.
- 23. The system of claim 22 wherein said scaling circuit uses a voltage reference to establish scaling of an input signal voltage swing to an output signal voltage swing to make the output signal compatible to operate at the second supply voltage.
RELATED APPLICATIONS
[0001] This application claims priority from U.S. Provisional Patent Application Serial No. 60/269,068, entitled “High Impedance Current Mode Voltage Scalable Driver” filed Feb. 15, 2001.
Provisional Applications (1)
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Number |
Date |
Country |
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60269068 |
Feb 2001 |
US |