Continuous open loop control to closed loop control transition

1. A transmission circuit, comprising:

a variable gain amplifier configured to receive a radio frequency (RF) modulated signal, wherein an output power of the RF signal is adjusted in an open loop mode control by changing a gain of the variable gain amplifier in accordance with a pre-specified reference value;

a subtraction block configured to receive an output of the variable gain amplifier and a scaled-up version of the RF modulated signal generated by modifying the RF modulated signal, and to generate a measurement loop error as the difference between the output of the variable gain amplifier and the scaled-up version of the RF modulated signal;

a controller configured to receive and measure the measurement loop error in the open loop mode control, and to generate a correction applied to prevent error when transitioning to the closed loop mode control;

an absolute value generator configured to receive the RF modulated signal and to generate an absolute representation of the RF modulated signal; and

a programmable amplifier located downstream of the absolute value generator and configured to scale up a received signal to generate the scaled-up version of the RF modulated signal based upon the pre-specified reference value.

2. The transmission circuit of claim 1 , wherein the controller includes one or more accumulators or integrators.

3. The transmission circuit of claim 1 , wherein the closed loop mode control includes generating an integrated error signal.

4. The transmission circuit of claim 1 , further comprising:

a multiplier configured to mix the pre-specified reference value with the correction to generate a corrected reference value that is applied to the variable gain amplifier in a closed loop control mode.

5. The transmission circuit of claim 1 , wherein the RF modulated signal is modified as a function of the pre-specified reference value to generate the scaled-up version of the RF modulated signal that is provided to the subtraction block.

6. The transmission circuit of claim 1 , wherein the subtraction block is configured to generate the measurement loop error by adjusting a value of the scaled-up version of the RF modulated signal to be equal to a value of the output of the variable gain amplifier when transitioning from the open loop mode control to a closed loop mode control, thereby setting the measurement loop error equal to zero at a time of the transition.

7. The transmission circuit of claim 1 , further comprising:

a low pass filter coupled between the absolute value generator and the programmable amplifier and configured to receive the RF modulated signal.

8. A method for power control comprising:

receiving an input signal at a transmission section;

checking whether a power control loop is active;

comparing a transition constant of the power control loop with a scaled baseband (BB) input signal to determine whether to control power of a received radio frequency (RF) signal by open loop mode or by closed loop mode; and

if the power control loop is active, controlling the output power of the received RF signal by the closed loop mode in which output power is controlled by multiplication of a reference signal with an error signal generated as a difference between a measured output signal of the transmission section and a modification of the input signal of the transmission section;

if the power control loop mode is not active, controlling the output power of the received RF signal by the open loop mode in which output power is controlled by the reference signal.

9. The method of claim 8 , wherein the received RF signal is a modulated and amplified signal.

10. The method of claim 8 , wherein the open loop mode is controlled by a reference signal.

11. The method of claim 8 , wherein generating the error signal further comprises adjusting a first value of the scaled input signal to be equal to a second value of the detected output signal when transitioning from open loop mode to closed loop mode, thereby setting the error signal equal to zero at a time of the transition.

12. A method for closed loop power control comprising:

detecting an output signal of a variable gain amplifier;

generating an error signal by subtracting the detected output signal from a scaled version of an input signal that is input to the variable gain amplifier, wherein the scaled input signal is generated by amplifying an input signal to the transmission circuit with a programmable amplifier;

integrating the error signal;

multiplying the integrated error signal with a reference signal to generate a control signal,

wherein generating the scaled input signal further comprises:

receiving the input signal to the transmission circuit;

passing the input signal through an absolute value generator to generate an absolute representation of the input signal;

filtering the absolute representation of the input signal through a band pass filter; and

amplifying the filtered absolute representation of the input signal with a programmable amplifier.

13. The method of claim 12 , wherein generating the error signal comprises using an input from an open loop control mode.

14. The method of claim 13 , wherein generating the error signal further comprises adjusting a first value of the scaled input signal to be equal to a second value of the detected output signal when transitioning from open loop mode to closed loop mode, thereby setting the error signal equal to zero at a time of the transition.

15. A transmission circuit in a communication device that provides a transition of power signal control from open loop mode to closed loop mode comprising:

a modulator that receives a baseband (BB) signal, and modulates the baseband signal to a radio frequency (RF) signal, wherein output power of the RF signal may be adjusted by open loop control or closed loop control;

a comparator that compares a transition constant of the power control loop with a reference value to determine a transition between the open loop mode and the closed loop mode;

a power control loop (PCL) that operates in the closed loop mode, the PCL comprising:

a variable gain amplifier (VGA) having a gain that is adjusted to regulate the output power of the RF signal;

a low-pass filter that removes noise from output of the VGA; and

a divider circuit to accommodate a wide output power bandwidth; and

a reference adjustment loop (RAL) that operates in the open loop mode,

wherein the transmission circuit is part of a mixed-signal system, and the PCL comprises multiple variable gain amplifiers having gains that are adjusted to regulate the output power of the RF signal.

16. The method of claim 12 , wherein the scaled input signal further comprises an analog or digital baseband signal.