Closed-loop high voltage booster
View Patent ↗A voltage boosting circuit with a closed-loop control mechanism and a controllable slew rate. A tracking capacitor and a control current form the closed-loop and are used to adjust the slew rate of the boosting circuit. The closed-loop control and adjustable slew rate improve the accuracy and predictability of the boosting circuit's final boosted output voltage.
1. A voltage boosting circuit comprising:
means for pre-charging a boosting capacitor to a pre-charge voltage;
means for boosting the pre-charge voltage at the capacitor;
means for tracking a boosted voltage at an output node connected to the boosting capacitor; and
means for feeding back a feedback voltage indicative of the boosted voltage to said boosting means,
wherein said boosting means comprises a voltage-to-current converter, said converter having a first input connected to a reference voltage, a second input connected to the feedback voltage, and an output current based on a difference between the reference voltage and the feedback voltage.
2. The boosting circuit of claim 1 , wherein said pre-charging means comprises a pre-charge circuit.
3. The boosting circuit of claim 1 , wherein said voltage-to-current converter comprises:
a current source outputting a control current; and
a differential circuit controlled by said control current.
4. The boosting circuit of claim 1 , wherein said voltage-to-current converter comprises:
a current source outputting a control current; and
an integrator controlled by said control current.
5. The boosting circuit of claim 1 , wherein said tracking means comprises a capacitor.
6. A pixel cell for an imager, said pixel cell comprising:
a first transistor having its gate connected to a control voltage; and
a voltage boosting circuit outputting said control voltage to said first transistor, said boosting circuit comprising:
means for pre-charging a boosting capacitor to a pre-charge voltage;
means for boosting the pre-charge voltage at the capacitor;
means for tracking a boosted voltage at an output node connected to the boosting capacitor; and
means for feeding back a feedback voltage indicative of the boosted voltage to said boosting means,
wherein said boosting means comprises a voltage-to-current converter, said converter having a first input connected to a reference voltage, a second input connected to the feedback voltage, and an output current based on a difference between the reference voltage and the feedback voltage.
7. The pixel cell of claim 6 , wherein said pre-charging means comprises a pre-charge circuit.
8. The pixel cell of claim 6 , wherein said voltage-to-current converter comprises:
a current source outputting a control current; and
a differential circuit controlled by said control current.
9. The pixel cell of claim 6 , wherein said voltage-to-current converter comprises:
a current source outputting a control current; and
an integrator controlled by said control current.
10. The pixel cell of claim 6 , wherein said tracking means comprises a capacitor.
11. An imager comprising:
a pixel cell, said pixel cell comprising a first circuit element connected to a boosted voltage, and a voltage boosting circuit outputting said boosted voltage to said first transistor, said boosting circuit comprising:
means for pre-charging a boosting capacitor to a pre-charge voltage;
means for boosting the pre-charge voltage at the capacitor;
means for tracking a boosted voltage at an output node connected to the boosting capacitor; and
means for feeding back a feedback voltage indicative of the boosted voltage to said boosting means,
wherein said boosting means comprises a voltage-to-current converter, said converter having a first input connected to a reference voltage, a second input connected to the feedback voltage, and an output current based on a difference between the reference voltage and the feedback voltage.
12. A method of providing a boosted voltage, said method comprising the steps of:
pre-charging a circuit to a pre-charge voltage;
boosting the pre-charge voltage;
tracking a level of the boosted voltage; and
using a voltage indicative of the level of the boosted voltage to control said boosting step until the boosted voltage reaches a predetermined level, said using step comprising:
comparing a reference voltage to the voltage indicative of the level of the boosted voltage,
generating a current based on a difference between the reference voltage to the voltage indicative of the level of the boosted voltage, and
applying the generated current to the circuit.
13. The method of claim 12 , wherein the voltage indicative of the level of the boosted voltage is a difference between the boosted voltage and the pre-charge voltage.
14. The method of claim 12 , wherein said tracking step comprises obtaining a difference between the pre-charge voltage and the boosted voltage.
15. The method of claim 12 , wherein said pre-charging step comprises applying a pre-charge voltage to a first electrode of a capacitor.
16. The method of claim 15 , wherein said boosting step comprises applying a current to a second electrode of the capacitor.