Internal calibration system for a radio frequency (RF) transmitter

1. A method for internally calibrating a radio frequency (RF) transmitter, comprising:

generating within a radio frequency (RF) transmitter a first set of test points at which an output of the RF transmitter is measured, wherein each member of the first set of test points resides along a perimeter of a square trajectory in an in-phase and quadrature phase signal space, a subgroup of the test points located at respective corners of the square trajectory;

measuring the radio frequency output of the RF transmitter at the first set of test points;

generating estimates of a phase imbalance and a DC offset in a quadrature dimension from the radio frequency output of the RF transmitter;

applying the estimates of the phase imbalance and the DC offset in the quadrature dimension to a compensator;

measuring the radio frequency output of the RF transmitter resulting from applying the estimates to the compensator at a second set of test points, the second set of test points being a subset of the first set of test points and including a single member from the subgroup of test points;

calculating a gain imbalance resulting from measuring the radio frequency output of the RF transmitter resulting from applying the second set of test points;

applying the gain imbalance to the compensator;

measuring the radio frequency output of the RF transmitter resulting from applying the gain imbalance to the compensator;

calculating a DC offset in an in-phase dimension from measuring the radio frequency output of the RF transmitter resulting from applying a third set of test points, the third set of test points being a subset of the first set of test points and a subset of the second set of test points; and

compensating for the measured DC offset in the in-phase dimension.

2. The method of claim 1 , wherein measuring the radio frequency output of the RF transmitter is accomplished using an energy detector.

3. The method of claim 1 , wherein the first and second sets of test points are generated using a transmitter output scaled by a scaling factor.

4. The method of claim 3 , wherein the scaling factor is unity.

5. The method of claim 1 , wherein the first set of test points comprises six test points.

6. The method of claim 1 , wherein the second set of test points comprises four test points.

7. The method of claim 1 , wherein the third set of tests points comprises two test points.

8. An internal calibration system for a radio frequency (RF) transmitter, comprising:

a digital processing element to generate within a radio frequency (RF) transmitter a set of test points at which an output of the RF transmitter is measured, wherein each member of the set of tests points resides along a perimeter of a square trajectory in an in-phase and quadrature phase signal space, a subgroup of test points located at respective corners of the square trajectory;

an RF detector to measure the radio frequency output of the RF transmitter at the test points, the digital processing element also determining transmitter impairments by analyzing the measured radio frequency output, wherein analyzing comprises evaluating the output of the RF transmitter at the test points; and

compensation circuitry to compensate the RF transmitter for the transmitter impairments.

9. The system of claim 8 , wherein the RF detector is implemented using an energy detector.

10. The system of claim 9 , wherein the digital processing element generates the test points using a transmitter output scaled by a scaling factor.

11. The system of claim 10 , wherein the scaling factor is unity.

12. The system of claim 8 , wherein the first compensation step is responsive to six measurements of the output of the RF transmitter corresponding to six test points.

13. The system of claim 8 , wherein the second compensation step is responsive to four measurements of the output of the RF transmitter corresponding to four test points.

14. The system of claim 8 , wherein the third compensation step is responsive to two measurements of the output of the RF transmitter corresponding to two test points.

15. A portable transceiver having an internal calibration system for a radio frequency (RF) transmitter, comprising:

transmit and receive circuitry;

a digital processing element to generate within a radio frequency (RF) transmitter a set of test points at which an output of the RF transmitter is measured, wherein each member of the first set of test points resides along a perimeter of a square trajectory in an in-phase and quadrature phase signal space, a subgroup of test points located at respective corners of the square trajectory;

an RF detector to measure the radio frequency output of the RF transmitter at the test points, the digital processing element also determining transmitter impairments by analyzing the measured radio frequency output, wherein analyzing comprises evaluating the output of the RF transmitter at test points; and

compensation circuitry to compensate the RF transmitter for the transmitter impairments.