Closed loop control in a camera module
A system may include an output stage for driving a load at an output of the output stage, a pulse-width modulation mode path configured to pre-drive the output stage in a first mode of operation, a linear mode path configured to pre-drive the output stage in a second mode of operation and a loop filter coupled at its input to the output of the output stage and coupled at its output to both of the pulse-width modulation mode path and the linear mode path. The pulse-width modulation mode path and the linear mode path may be configured such that a first transfer function between the output of the loop filter and the output of the output stage is substantially equivalent to a second transfer function between the output of the loop filter and the output of the output stage.
1. A system comprising:
an output stage for driving a load at an output of the output stage;
a pulse-width modulation mode path configured to pre-drive the output stage in a first mode of operation;
a linear mode path configured to pre-drive the output stage in a second mode of operation; and
a loop filter, wherein an input of the loop filter is coupled to the output of the output stage and wherein an output of the loop filter is coupled to both of the pulse-width modulation mode path and the linear mode path;
wherein the pulse-width modulation mode path and the linear mode path are configured such that a first transfer function between the output of the loop filter and the output of the output stage through the pulse-width modulation mode path is substantially equivalent to a second transfer function between the output of the bop filter and the output of the output stage through the linear mode path,
such that an output of the loop filter after switching between the first mode of operation and the second mode of operation settles to approximately the same value as the output of the loop filter before switching between the first mode of operation and the second mode of operation.
2. The system of claim 1 , wherein the pulse-width modulation mode path comprises a pulse-width modulation quantizer and a pulse-width modulation pre-driver to the output stage.
3. The system of claim 1 , wherein the linear mode path comprises a linear pre-driver to the output stage.
4. The system of claim 1 , wherein the output stage comprises a voltage driver in both the first mode of operation and the second mode of operation.
5. The system of claim 1 , wherein:
the loop filter is configured to output a proportional voltage required to generate a desired output current at the output of the output stage;
in the first mode of operation, the proportional voltage is quantized and buffered by the pulse-width mode modulation path and the output stage to generate the desired output current; and
in the second mode of operation, the proportional voltage is buffered by the linear mode path and the output stage to generate the desired output current.
6. The system of claim 5 , wherein in the first mode of operation, the proportional voltage is quantized, buffered, and amplified by the pulse-width mode modulation path and the output stage to generate the desired output current.
7. The system of claim 5 , wherein in the second mode of operation, the proportional voltage is buffered and amplified by the linear mode path and the output stage to generate the desired output current.
8. The system of claim 1 , wherein the load comprises a motor within a camera module for controlling a position associated with a camera of the camera module.
9. The system of claim 8 , wherein an input of the loop filter is indicative of a current for driving the motor.
10. A method comprising:
in a first mode of operation, pre-driving with a pulse-width modulation mode path an output stage for driving a load at an output of the output stage;
in a second mode of operation, pre-driving the output stage with a linear mode path; and
filtering an output signal with a loop filter, wherein an input of the loop filter is coupled to the output of the output stage and wherein an output of the loop filter is coupled to both of the pulse-width modulation mode path and the linear mode path;
wherein the pulse-width modulation mode path and the linear mode path are configured such that a first transfer function between the output of the loop filter and the output of the output stage through the pulse-width modulation mode path is substantially equivalent to a second transfer function between the output of the loop filter and the output of the output stage through the linear mode path,
such that an output of the loop filter after switching between the first mode of operation and the second mode of operation settles to approximately the same value as the output of the loop filter before switching between the first mode of operation and the second mode of operation.
11. The method of claim 10 , wherein the pulse-width modulation mode path comprises a pulse-width modulation quantizer and a pulse-width modulation pre-driver to the output stage.
12. The method of claim 10 , wherein the linear mode path comprises a linear pre-driver to the output stage.
13. The method of claim 10 , wherein the output stage comprises a voltage driver in both the first mode of operation and the second mode of operation.
14. The method of claim 10 , further comprising:
outputting by the loop filter a proportional voltage required to generate a desired output current at the output of the output stage;
in the first mode of operation, quantizing and buffering the proportional voltage by the pulse-width mode modulation path and the output stage to generate the desired output current; and
in the second mode of operation, buffering the proportional voltage by the linear mode path and the output stage to generate the desired output current.
15. The method of claim 14 , further comprising in the first mode of operation, amplifying the proportional voltage by the pulse-width mode modulation path and the output stage to generate the desired output current.
16. The method of claim 14 , further comprising in the second mode of operation, amplifying the proportional voltage by the linear mode path and the output stage to generate the desired output current.
17. The method of claim 10 , wherein the load comprises a motor within a camera module for controlling a position associated with a camera of the camera module.
18. The method of claim 17 , wherein an input of the loop filter is indicative of a current for driving the motor.
19. The method of claim 10 , wherein a feedback path, from the output of the output stage to the input of the loop filter, comprises a current monitor and a combiner, and wherein a transfer function of the feedback path is approximately the same when operating in the first mode of operation and when operating in the second mode of operation.
20. The system of claim 1 , comprising a feedback path from the output of the output stage to the input of the loop filter, wherein the feedback path comprises a current monitor and a combiner, and wherein a transfer function of the feedback path is approximately the same when operating in the first mode of operation and when operating in the second mode of operation.