Digital matching of a radio frequency antenna

• US 9,825,659 B2
• Filed: 06/02/2015
• Issued: 11/21/2017
• Est. Priority Date: 06/03/2014
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Robey, Frank C., Hancock, Timothy M., Stahl, Gregory B.
• Primary Examiner(s): Joseph, Jaison
• Application Number:
  US14/916,376
• Publication Number:
  US 20160218759A1
• Time in Patent Office: 903 Days
• CPC Class Codes: H04B 1/1027 assessing signal quality or detecting noise/interference for the received signal
• CPC Class Codes: H04B 1/18 Input circuits, e.g. for coupling to an antenna or a transmission line coupling networks between antennas or lines and receivers independent of the nature of the receiver H03H
• CPC Class Codes: H04B 17/21 for calibration; for correcting measurements
• CPC Class Codes: H04B 17/336 Signal-to-interference ratio [SIR] or carrier-to-interference ratio [CIR]

Abstract

A matching technique that may be used with electrically small antennas uses one or more digital circuit blocks connected in a feedback arrangement configured to tune the transfer function response between the antenna and an output port of the system. Each circuit block may include an analog-to-digital converter (ADC), a digital filter, and a digital-to-analog converter (DAC). As such, tuning the transfer function may be achieved by sensing a voltage or current at various circuit nodes using one or more ADCs, filtering the measurements in response-shaping digital filters, and using one or more DACs to drive other circuit nodes in a manner that elicits a desired circuit response. Techniques are provided for allowing a matched antenna to adapt to a changing environment about the antenna. In one illustrative embodiment, the digital circuit blocks may be provided as digital non-Foster circuit blocks.

Claims

1. An antenna system, comprising:

an antenna;

receiver circuitry to process signals received by the antenna, the receiver circuitry including a first electronic component having an input coupled to a port of the antenna; and

matching circuitry to tune a transfer function between the antenna and the first electronic component, the matching circuitry including a digital circuit block to implement matching, the digital circuit block being coupled to provide feedback to the port of the antenna, wherein the digital circuit block includes;

an analog-to-digital converter (ADC) to convert a sensed analog input signal to a digital output signal;

a digital processor to process the digital output signal of the ADC in accordance with a transfer function associated with a matching scheme; and

a digital-to-analog converter (DAC) to convert a digital output signal of the digital processor to an analog signal.

2. The antenna system of claim 1, wherein:

the ADC of the digital circuit block samples a signal on a node of the receiver circuitry after the first electronic component; and

the DAC of the digital circuit block injects an analog signal at the input of the first electronic component.

3. The antenna system of claim 1, wherein:

the matching circuitry includes multiple digital circuit blocks, wherein each of the multiple digital circuit blocks implements a different transfer function within a corresponding digital processor and provides feedback to the antenna port by a different mechanism.

4. The antenna system of claim 1, wherein:

the matching circuitry includes at least two digital circuit blocks that are cross coupled with one another in a manner that combines different sensing modes with different feedback mechanisms.

5. The antenna system of claim 1, wherein:

the matching circuitry is configured to adapt to a changing environment around the antenna to tune the transfer function between the antenna and the first electronic component.

6. The antenna system of claim 5, wherein the matching circuitry further comprises:

a waveform source for imparting a probe waveform to a node associated with the first electronic component and the antenna; and

a monitor for monitoring a response of the first electronic component and/or the antenna to the probe waveform.

7. The antenna system of claim 6, wherein the matching circuitry further comprises:

a system model generator to generate a system model based on the response of the first electronic component and/or the antenna to the probe waveform; and

a filter modification unit to modify the transfer function associated with the digital non-Foster circuit block based, at least in part, on the system model.

8. The antenna system of claim 7, wherein the system model is a linear model.

9. The antenna system of claim 7, wherein the system model includes both linear and non-linear responses.

10. The antenna system of claim 7, wherein the transfer function is used to maximize signal to noise ratio at an antenna system output port.

11. The antenna system of claim 7, wherein the transfer function is used to minimize signal distortion at an antenna system output port.

12. The antenna system of claim 6, wherein the matching circuitry further comprises:

a system model generator to generate a system model based on the response of the antenna and/or first electronic component to the probe waveform;

a compensation filter of the probe waveform to generate an output signal representative of a response of the antenna and first electronic component to the probe waveform; and

a difference unit to subtract the signal representative of the probe waveform response from an output signal of the first electronic component.

13. The antenna system of claim 6, further comprising means to activate and deactivate the waveform source.

14. The antenna system of claim 6, wherein:

the waveform source is configured to generate a probe waveform having a bandwidth that encompasses an operational bandwidth of the antenna system.

15. The antenna system of claim 6, wherein:

the waveform source is configured to generate a probe waveform having a relatively high signal level and a short duration.

16. The antenna system of claim 6, wherein:

the waveform source is configured to generate a probe waveform having a relatively low signal level that is continuously applied to the node during antenna operation.

17. The antenna system of claim 1, wherein:

the ADC and the DAC are configured to operate in a sub-sampling mode and the matching circuitry is configured to perform matching operations in Nyquist zones greater than a first Nyquist zone.

18. The antenna system of claim 1, wherein:

the digital processor is programmed with instructions to process the digital output signal of the ADC in accordance with a transfer function associated with a matching scheme.

19. The antenna system of claim 18, wherein the instructions to process the digital output in accordance with a transfer function that include at least one of a maximum power transfer (non-Foster), maximum signal-to-noise ratio, maximum dynamic range, and/or other matching schemes and transfer functions that can be adaptively, controllably programmed with precise tolerances beyond those inherent with an analog-based matching scheme.

20. The antenna system of claim 1, wherein:

the matching circuitry includes multiple digital non-Foster circuit blocks, wherein each of the multiple digital non-Foster circuit blocks implements a different transfer function within a corresponding digital processor and provides feedback to the antenna port by a different mechanism.

21. The antenna system of claim 1, wherein:

the matching circuitry includes at least two digital non-Foster circuit blocks that are cross coupled with one another in a manner that combines different sensing modes with different feedback mechanisms.

22. The antenna system of claim 21, wherein the matching circuitry further comprises:

a system model generator to generate a system model based on the response of the first electronic component and/or the antenna to the probe waveform; and

a filter modification unit to modify the transfer function associated with the digital non-Foster circuit block based, at least in part, on the system model.

23. The antenna system of claim 22, wherein the system model includes one or more of:

a linear model;

both linear and non-linear responses.

24. The antenna system of claim 22, wherein the transfer function operates to perform at least one of:

increasing signal to noise ratio at an antenna system output port; and

reducing signal distortion at an antenna system output port.

25. A method for tuning a transfer function between an antenna and an electronic component, the method comprising:

sampling and digitizing a signal at a circuit node in an antenna system having an antenna coupled to a first electronic component;

filtering the digitized signal in a digital filter to generate a filtered digital signal;

converting the filtered digital signal to an analog signal and feeding the analog signal back to a node associated with the antenna, wherein the digital filter includes a transfer function that is designed to provide non-Foster matching between the antenna and the first electronic component;

superimposing a probe waveform onto the analog signal that is fed back to the node associated with the antenna;

monitoring a response of the antenna and/or the first electronic component to the probe waveform; and

modifying the transfer function of the digital filter based on the response of the antenna and/or the first electronic component to the probe waveform to maintain a desired condition between the antenna and the first electronic component when an environment about the antenna is changing.

26. The method of claim 25, further comprising:

continually repeating superimposing, monitoring, and modifying during operation of the antenna system.

27. The method of claim 25, wherein:

superimposing includes adding a digital version of the probe waveform to the filtered digital signal before converting the filtered digital signal to an analog signal.

28. The method of claim 25, wherein:

the transfer function of the digital filter is computed in accordance with one of the following goals;

optimizing power transfer, optimizing SNR, suppressing undesired receive signals, and suppressing undesired non-linear circuit responses.

29. The method of claim 25, wherein:

the digital filter includes a first digital filter and the filtered digital signal includes a first filtered digital signal; and

the method further comprises;

filtering the digitized signal in a second digital filter to generate a second filtered digital signal; and

converting the second filtered digital signal to a second analog signal and feeding the second analog signal back to a node associated with the antenna, wherein the second digital filter includes a second transfer function that is designed to provide non-Foster matching between the antenna and the first electronic component.

30. The method of claim 25, wherein:

the circuit node in the antenna system includes a first circuit node; and

the method further comprises;

sampling and digitizing a second signal at a second circuit node in the antenna system to generate a second digitized signal;

filtering the second digitized signal in a second digital filter to generate a second filtered digital signal; and

converting the second filtered digital signal to a second analog signal and feeding the second analog signal back to the same or a different node associated with the antenna, wherein the second digital filter includes a second transfer function that is designed to provide non-Foster transfer function tuning between the antenna and the first electronic component.

31. An antenna system, comprising:

a multiport antenna;

receiver circuitry to process signals received by the multiport antenna, the receiver circuitry including a first electronic component having an input coupled to one or more ports of the antenna; and

matching circuitry to tune a transfer function between the multiport antenna and the first electronic component, the matching circuitry including a digital non-Foster circuit block to implement non-Foster matching, the digital non-Foster circuit block being coupled to provide feedback to at least one port of the multiport antenna so that the antenna forms a portion of the feedback loop, wherein the digital non-Foster circuit block includes;

an analog-to-digital converter (ADC) to convert a sensed analog input signal to a digital output signal;

a digital processor to process the digital output signal of the ADC in accordance with a transfer function associated with a non-Foster matching scheme; and

a digital-to-analog converter (DAC) to convert a digital output signal of the digital processor to an analog signal.

32. The antenna system of claim 31, wherein:

the matching circuitry includes one DAC for each of at least two ports of the antenna for use in providing feedback.

33. The antenna system of claim 31, wherein:

the multiport antenna includes multiple coils wrapped about a common magnetic core, wherein each coil defines a port of the antenna and the magnetic core forms a feedback summing junction wherein the multiple coils are configured to achieve a desired flux combining ratio.

34. The antenna system of claim 31, wherein:

the multiport antenna includes distributed capacitive coupling structures to serve as a feedback summing junction, wherein one or more feedback signals are coupled through an electric field within the distributed capacitive coupling.