Apparatus for generation of corrected vector wideband RF signals

• US 9,621,286 B2
• Filed: 06/29/2011
• Issued: 04/11/2017
• Est. Priority Date: 06/29/2011
• Status: Active Grant

• Current Assignee: Tektronix Incorporated (Fortive Corp.)
• Original Assignee: Tektronix Incorporated (Fortive Corp.)
• Inventors: Earls, Jeffrey D.
• Primary Examiner(s): Lugo, David B.
• Application Number:
  US13/172,541
• Publication Number:
  US 20130003889A1
• Time in Patent Office: 2,113 Days
• Field of Search: 375296, 375297, 4551143
• CPC Class Codes: H04B 17/0085 using test signal generators
• CPC Class Codes: H04B 17/11 for calibration

Abstract

A signal generation system can include an input source configured to provide an input radio frequency (RF) signal, a correction filter calculation (CFC) block configured to determine correction filter parameters, and an automatic level control (ALC) loop configured to provide ALC loop information to the CFC block. The correction filter parameters may be determined based at least in part on the ALC information. The system can also include a predistortion field programmable gate array (FPGA) configured to apply a correction filter to the input RF signal, wherein the correction filter is based at least in part on the correction filter parameters, and an RF output configured to provide an RF output signal.

Claims

1. A signal generation system, comprising:

an input source configured to provide an input signal;

a calibration memory configured to store calibration data pertaining to an analog channel performance of the signal generation system across various frequencies and system settings of the signal generation system, wherein the calibration data includes an effect of various automatic level control attenuator settings on the analog channel performance;

a correction filter calculation block configured to determine correction filter parameters for the signal generation system based on the calibration data;

a predistortion component configured to receive the input signal and correction filter parameters and generate a filtered output signal through application of a correction filter to the input signal, wherein the correction filter is based at least in part on the correction filter parameters; and

an automatic level control loop including;

an automatic level control attenuator configured to receive the filtered output signal and output an attenuated output signal, and

an automatic level control controller configured to provide an indicator of a current setting of the automatic level control attenuator to the correction filter calculation block, wherein the correction filter parameters are further determined based at least in part on the current setting of the automatic level control attenuator.

2. The signal generation system of claim 1, wherein the input source is a memory-based data generation block, a digital in-phase and quadrature (I/Q) input, or an analog I/Q input.

3. The signal generator system of claim 2, wherein the correction filter is a first correction filter, and further comprising a second correction filter, wherein the predistortion component is further configured to apply the first correction filter to an in-phase component of the input signal and the second correction filter to a quadrature component of the input signal, and wherein the second correction filter is also based at least in part on the correction filter parameters.

4. The signal generation system of claim 1, wherein the attenuated output signal is a first attenuated output signal, the signal generation system further comprising:

an output attenuator configured to receive the attenuated output signal from the automatic level control attenuator and output a second attenuated output signal; and

a radio frequency output configured to provide a radio frequency output signal based on the second attenuated output signal.

5. The signal generation system of claim 1, further comprising:

a power detector configured to provide the automatic level control controller with power information pertaining to the attenuated output signal, wherein the automatic level control controller is further configured to adjust settings of the automatic level control attenuator, based on the power information, to cause the automatic level control attenuator to maintain a constant output power level.

6. The signal generation system of claim 5, wherein the automatic level control controller is further configured to update the indicator of the current setting of the automatic level control loop attenuator to reflect the adjusted settings of the automatic level control attenuator, and wherein the correction filter calculation block is further configured to update the correction filter parameters to reflect the adjusted settings of the automatic level control attenuator.

7. The signal generation system of claim 1, further comprising:

a digital-to-analog converter configured to generate an analog output signal based on the filtered output signal.

8. The signal generation system of claim 7, further comprising:

an RF modulator coupled between the digital-to-analog converter and the automatic level control attenuator.

9. The signal generation system of claim 8, further comprising:

an intermediate filter coupled between the digital-to-analog converter and the RF modulator.

10. The signal generation system of claim 1, wherein the predistortion component comprises a field programmable gate array.

11. The signal generation system of claim 1, wherein the predistortion component comprises an application-specific integrated circuit.

12. The signal generation system of claim 1, wherein the calibration data is measured at a factory and includes vector data describing amplitude flatness and phase linearity at each frequency setting for one or more of the various automatic level control attenuator settings.

13. A method for correcting radio frequency (RF) signals in a signal generation system, the method comprising:

receiving an input RF signal from an input source;

receiving, by a correction filter calculation block, an indicator of a current setting of an automatic level control attenuator;

receiving, by the correction filter calculation block, calibration data pertaining to an analog channel performance of the signal generation system across various frequencies and system settings of the signal generation system, the calibration data including an effect of various automatic level control attenuator settings on the analog channel performance;

determining, by the correction filter calculation block, correction filter parameters based at least in part on the indicator of the current setting of the automatic level control attenuator and the calibration data and

generating, by a predistortion component, a filtered RF signal by applying a correction filter to the input RF signal, wherein the correction filter is based on the correction filter parameters.

14. The method of claim 13, wherein the input RF signal has in-phase and quadrature signal components, and wherein the generating a filtered RF signal step further comprises generating respective in-phase and quadrature filtered RF signals by applying an in-phase component correction filter to the in-phase signal component of the input RF signal and a quadrature component correction filter to the quadrature signal component of the input RF signal, wherein the in-phase component correction filter and the quadrature component correction filter are both based on the correction filter parameters.

15. The method of claim 13, further comprising:

receiving, by an automatic level control controller, RF power information pertaining to an output of the automatic level control attenuator;

adjusting automatic level control attenuator settings to cause the automatic level control attenuator to maintain a constant output power level;

updating the indicator of the current setting of the automatic level control attenuator to reflect the adjusted automatic level control attenuator settings;

re-determining the control filter parameters based on the updated indicator; and

generating an updated filtered RF signal by applying an updated correction filter to the input RF signal, wherein the updated correction filter is based on the re-determined correction filter parameters.

16. The method of claim 13, further comprising:

providing the filtered RF signal to an RF modulator; and

generating an RF signal modulated by the filtered RF signal.

17. The method of claim 16, wherein the filtered RF signal comprises in-phase and quadrature signal components.

18. One or more non-transitory computer-readable media having instructions stored thereon which, when executed by one or more processors of a signal generation system cause the signal generation system to:

receive an input signal from an input source;

receive an indicator of a current setting of an automatic level control attenuator;

receive calibration data pertaining to an analog channel performance of the signal generation system across various frequencies and system settings of the signal generation system, the calibration data including an effect of various automatic level control attenuator settings of the automatic level control attenuator on the analog channel performance;

determine correction filter parameters based at least in part on the current setting of the automatic level control attenuator and the calibration data; and

generate a filtered signal by applying a correction filter to the input signal, wherein the correction filter is based on the correction filter parameters.

19. The one or more non-transitory computer-readable media of claim 18, wherein the instructions, when executed by the one or more processors, further cause the signal generation system to:

receive power information pertaining to an output of the automatic level control attenuator;

adjust the current setting of the automatic level control attenuator to cause the automatic level control attenuator to maintain a constant output power level;

update the indicator to reflect the adjusted current setting of the automatic level control attenuator;

re-determine the control filter parameters based on the updated indicator; and

generate an updated filtered signal by applying an updated correction filter to the input signal, wherein the updated correction filter is based on the re-determined correction filter parameters.

20. The one or more non-transitory computer-readable media of claim 18, wherein the calibration data was measured at a factory and includes vector data describing amplitude flatness and phase linearity at each frequency setting for each of the various automatic level control attenuator settings.