Circuit for voltage controlled oscillator
View Patent ↗A voltage controlled oscillator and a load cell circuit usable in VCO are provided. The VCO features an internal compensation for process, voltage and temperature using a replica of half of the oscillating stage. The load cell circuit comprises a bias transistor to drain a predetermined current from the oscillating stage, a control transistor to vary resistance offered by it responsive to a control voltage applied and a resistor adapted to provide a clamp resistance.
1. A Voltage Controlled Oscillator (VCO) including at least one load cell circuit, the load cell circuit comprising:
a bias transistor adapted to drain a predetermined current from an oscillating stage, wherein the bias transistor places the VCO in a particular operating range based on a bias voltage;
a control transistor adapted to vary resistance offered by it responsive to a control voltage applied, wherein the control transistor controls a frequency of oscillation of the VCO based on the control voltage;
a resistor adapted to provide a clamp resistance, the bias transistor, the control transistor and the resistor are arranged in parallel, and
the VCO further comprising a tail current source adapted to provide constant current to the oscillating stage.
2. The VCO of claim 1 wherein the resistor being a passive resistor.
3. The VCO of claim 1 wherein the control voltage is directly applied to the control transistor.
4. The VCO of claim 3 wherein the control voltage is not generated by a replica bias stage.
5. The VCO of claim 1 wherein a bias voltage is applied to the bias transistor.
6. The VCO of claim 5 wherein the bias voltage is generated by a bias stage.
7. The VCO of claim 6 wherein the bias voltage is passed from the bias stage to the load cell through a low pass filter.
8. The VCO of claim 6 wherein the bias stage comprises a replica load cell including a replica of the bias transistor, the load transistor and the resistor arranged in parallel.
9. The VCO of claim 8 wherein the bias voltage applied to the bias transistor of the load cell is derived from a bias transistor in the replica load cell.
10. The VCO of claim 9 wherein the bias voltage from the bias transistor in the replica load cell is supplied to the bias transistor of the load cell through a low pass filter.
11. The VCO of claim 8 wherein a gate voltage of the bias transistor in the replica load cell is derived from an output of an amplifier in positive feedback configuration, wherein a negative node of the amplifier is connected to a predetermined reference voltage, and a positive node is connected to a voltage across the replica load cell.
12. The VCO of claim 8 wherein a control voltage applied to a control transistor in the replica load cell is set to a predetermined value.
13. The VCO of claim 12 wherein the predetermined value is a constant value.
14. The VCO of claim 8 , wherein the VCO further comprises a replica tail current source adapted to provide constant current to the replica load cell.
15. The VCO of claim 14 , wherein the constant current of the replica tail current source is one half of a current level of the constant current of the tail current source.
16. A voltage controlled oscillator (VCO) comprising:
means for draining a predetermined current from an oscillating stage based on a bias voltage in order to place the VCO in a particular operating range;
means for varying resistance based on an applied control voltage, controlling a frequency of oscillation of the VCO based on the control voltage;
means for providing a clamp resistance; and
means for providing constant current to the oscillating stage; wherein the means for draining, the means for varying resistance, and the means for providing a clamp resistance are arranged in parallel.
17. The voltage controlled oscillator of claim 16 , further comprising:
means for providing a replica of the means for draining, means for varying resistance, and the means for providing a clamp resistance.
18. The voltage controlled oscillator of claim 16 , wherein the means for providing a replica includes a means for providing constant current to the means for providing a replica.
19. A method for operating a voltage controlled oscillator (VCO) comprising:
providing a first constant current to an oscillating stage of the voltage controlled oscillator; and
providing a variable control voltage to a load cell of the voltage controlled oscillator, wherein the load cell includes a bias transistor, a control transistor, and a resistor, arranged in parallel, wherein the variable control voltage controls a frequency of oscillation of the VCO through the control transistor.
20. The method of claim 19 , further comprising:
providing a second constant current to a replica load cell of the voltage controlled oscillator, wherein the second constant current is one half of the first constant current.