Receiver including a tracking filter

• US 8,725,103 B2
• Filed: 01/03/2012
• Issued: 05/13/2014
• Est. Priority Date: 01/03/2012
• Status: Active Grant

• Current Assignee: Silicon Laboratories Incorporated
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Koroglu, Mustafa H., Su, Yu
• Primary Examiner(s): PHU, SANH D
• Application Number:
  US13/342,548
• Publication Number:
  US 20130171954A1
• Time in Patent Office: 861 Days
• Field of Search: 455/307, 455/341, 455/245.1, 455/197, 455/302, 455/195
• US Class Current: 455/307
• CPC Class Codes: H03J 2200/32 Tuning of tracking filter
• CPC Class Codes: H04B 1/1027 assessing signal quality or detecting noise/interference for the received signal

Abstract

A receiver includes a low noise amplifier having an input for receiving a radio frequency signal, and an output. The receiver further includes a tracking filter having an input coupled to the output of the low noise amplifier. The tracking filter including a bandpass filter configured to pass the radio frequency signals. The bandpass filter includes a variable capacitor having a first electrode coupled to the input of the tracking filter for receiving the radio frequency signals, and a second electrode coupled to a power supply terminal. The bandpass filter further includes a transformer having a primary winding including a first terminal coupled to the first electrode of the variable capacitor and a second terminal coupled to a second power supply terminal. The transformer further includes a secondary winding.

Claims

1. A receiver comprising:

a low noise amplifier including an input for receiving a radio frequency signal and including an output; and

a tracking filter having an input coupled to the output of the low noise amplifier, the tracking filter including a bandpass filter configured to pass the radio frequency signals, the bandpass filter comprising;

a variable capacitor including a first electrode coupled to the input of the tracking filter for receiving the radio frequency signals, and a second electrode coupled to a power supply terminal; and

a transformer including a primary winding having a first terminal coupled to the first electrode of the variable capacitor and a second terminal coupled to a second power supply terminal, the transformer further including a secondary winding for providing an output of the tracking filter, wherein the secondary winding has an larger number of turns than the primary winding.

2. The receiver of claim 1, wherein the tracking filter further includes a second filter to pass frequencies of the radio frequency signal that are below a second threshold, the second filter comprising:

an inductor including a first terminal coupled to the input of the tracking filter, and a second terminal coupled to the power supply terminal;

a second variable capacitor including a first electrode coupled to the input of the tracking filter, and including a second electrode coupled to the power supply terminal;

a single-to-differential amplifier including an input coupled to the first electrode of the second variable capacitor, a first output, and a second output; and

a low-pass filter coupled between the first and second outputs.

3. The receiver of claim 2, wherein the low-pass filter comprises:

a second inductor including a first terminal coupled to the first output, and a second terminal;

a third inductor including a first terminal coupled to the second terminal of the second inductor, and a second terminal coupled to the second output; and

a third variable capacitor including a first electrode coupled to the first output and a second electrode coupled to the second output.

4. The receiver of claim 1, wherein a quality factor of the primary winding is greater than a quality factor of the secondary winding.

5. The receiver of claim 1, wherein:

the primary winding is formed from copper and aluminum; and

the secondary winding is formed from copper.

6. The receiver of claim 1, wherein the secondary winding is formed from a thinner metal than the primary winding.

7. The receiver of claim 1, wherein, when the secondary winding acts as a second-order inductive-capacitive low-pass filter.

8. A receiver comprising:

a low noise amplifier including an input for receiving a radio frequency signal and including an output; and

a tracking filter coupled to the output of the low noise amplifier and including a first filter configured to pass the radio frequency signals below a first frequency threshold, the first filter comprising;

a single-to-differential amplifier including an input coupled to the output of the low noise amplifier through a lowpass filter, and including a first output and a second output; and

a tracking bandpass filter coupled between the first and second outputs.

9. The receiver of claim 8, wherein the lowpass filter comprises:

an inductor including a first terminal coupled to the output of the low noise amplifier and a second terminal coupled to a power supply terminal; and

a variable capacitor including a first electrode coupled to the output of the low noise amplifier and a second electrode coupled to the power supply terminal.

10. The receiver of claim 8, wherein the tracking bandpass filter comprises:

a first inductor including a first terminal coupled to the first output, and a second terminal;

a second inductor including a first terminal coupled to the second terminal of the second inductor, and a second terminal coupled to the second output; and

a variable capacitor including a first electrode coupled to the first output and a second electrode coupled to the second output.

11. The receiver of claim 8, wherein the tracking filter includes a second filter comprising:

a variable capacitor including a first electrode coupled to the output of the low noise amplifier, and a second electrode coupled to a power supply terminal; and

a transformer including a primary winding having a first terminal coupled to the first electrode of the variable capacitor and a second terminal coupled to a second power supply terminal, the transformer further including a secondary winding having a first terminal and a second terminal.

12. The receiver of claim 11, wherein the second power supply terminal provides a mid-range voltage between power supply rails.

13. The receiver of claim 11, wherein the secondary winding includes more turns than the primary winding.

14. A tracking filter for use in a television receiver, the tracking filter comprising:

an input terminal for receiving a radio frequency signal;

a first filter including an input coupled to the input terminal and configured to pass frequencies below a first threshold, the first filter comprising;

a lowpass filter coupled to the input terminal;

a single-to-differential amplifier including an input coupled to the input terminal, and including a first output and a second output;

a band-pass filter coupled between the first and second outputs; and

a second filter including an input coupled to the input terminal and configured to pass frequencies between the first threshold and a second threshold.

15. The tracking filter of claim 14, wherein the lowpass filter comprises:

an inductor having a first terminal coupled to the input terminal, and a second terminal coupled to a power supply terminal; and

a variable capacitor including a first electrode coupled to the input terminal, and a second electrode coupled to the power supply terminal.

16. The tracking filter of claim 14, further comprising a third filter including:

variable capacitor including a first electrode coupled to the input terminal, and a second electrode coupled to a first power supply terminal; and

a transformer including a primary winding having a first terminal coupled to the first electrode of the variable capacitor and a second terminal coupled to a second power supply terminal, the transformer further including a secondary winding having a first terminal and a second terminal.

17. The tracking filter of claim 16, wherein the secondary winding includes more turns than the primary winding.

18. The tracking filter of claim 16, wherein the primary winding has a first quality factor that is higher than a second quality factor of the secondary winding.

19. The tracking filter of claim 18, wherein the secondary winding has an effect on the first quality factor that is inversely proportional to a fourth power of a tuned frequency.