Noise suppression in switching power supplies

• US 20040090802A1
• Filed: 11/01/2002
• Published: 05/13/2004
• Est. Priority Date: 11/01/2002
• Status: Abandoned Application

• Current Assignee: Sierra Wireless Incorporated
• Original Assignee: Sierra Wireless Incorporated
• Inventors: Hoang, Trong, Pourseyed, Behrouz
• Application Number:
  US10/285,980
• Publication Number:
  US 20040090802A1
• Time in Patent Office: Days
• US Class Current: 363/39
• CPC Class Codes: H02M 1/44 Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators

Abstract

A method and apparatus for suppressing noise caused by the switching of a switching power supply. The method and apparatus use frequency dithering techniques to distribute the switching noise and its spurious products over a wider bandwidth, thereby reducing the average peak power per given range of bandwidth. The frequency dithering techniques are particularly applicable to mobile radio applications, where switching noise from switching power supplies can modulate the transmit carrier and its harmonics, sub-harmonics and intermediate frequency products.

Claims

1. A switching power supply having noise suppression capabilities, comprising:

a switching regulator having a direct current (DC) voltage input, an oscillator input and a regulator output;

a filter having a first end coupled to the output of the switching regulator and a second end providing an output for the power supply;

a variable-frequency oscillator coupled to the oscillator input of the switching regulator, said variable-frequency oscillator having a frequency control input and an output that provides a variable-frequency oscillating signal; and

an alternating waveform generator coupled to the frequency control input of the variable-frequency oscillator.

2. The switching power supply of claim 1 wherein the alternating waveform generator comprises a square waveform generator and the control signal is a square wave control signal.

3. The switching power supply of claim 1 wherein the alternating waveform generator comprises a triangular waveform generator and the control signal is a triangular wave control signal.

4. The switching power supply of claim 1 wherein the filter comprises:

an inductor having a first end coupled to the output of the switching regulator and a second end providing the output of the power supply; and

a capacitor having a first end coupled to the second end of the inductor and a second end coupled to ground.

5. The switching power supply of claim 1 wherein the switching regulator and the variable-frequency oscillator comprise an integrated circuit.

6. The switching power supply of claim 1 wherein the switching regulator comprises:

a pulse width modulator (PWM) having a PWM oscillating signal input configured to accept the variable-frequency oscillating signal, a PWM control input, a PWM output and an inverted PWM output;

a high-side switch having a first terminal coupled to the DC voltage input, a second terminal coupled to the regulator output and a control input coupled to the PWM output;

a low-side switch having a first terminal coupled to ground, a second terminal coupled to the regulator output and a control input coupled to the inverted PWM output; and

a comparator having an inverting input coupled to the power supply output, a non-inverting input coupled to a reference voltage and an output coupled to the PWM control input.

7. A switching power supply having noise suppression capabilities, comprising:

a switching regulator having a direct current (DC) voltage input, an oscillator input and a regulator output;

a filter having a first end coupled to the output of the switching regulator and a second end providing an output for the power supply;

a variable-frequency oscillator coupled to the oscillator input of the switching regulator, said variable-frequency oscillator having a frequency control input and an output that provides a variable-frequency oscillating signal;

a first resistor having a first end coupled to the frequency control input of the variable-frequency oscillator and a second end coupled to ground;

a second resistor having a first end coupled to the frequency control input of the variable-frequency oscillator and a second end;

a switching element having a first terminal coupled to the second end of the second resistor, a second terminal coupled to ground and a control terminal; and

an alternating waveform generator coupled to the control terminal of the switching element operable to cause the switching element to intermittently couple the second end of the second resistor to ground.

8. The switching power supply of claim 7 wherein the filter comprises:

an inductor having a first end coupled to the output of the switching regulator and a second end providing the output of the power supply; and

a capacitor having a first end coupled to the second end of the inductor and a second end coupled to ground.

9. The switching power supply of claim 7 wherein the switching regulator and the variable-frequency oscillator comprise an integrated circuit.

10. The switching power supply of claim 7 wherein the switching regulator comprises:

a pulse width modulator (PWM) having a PWM oscillating signal input configured to accept the variable-frequency oscillating signal, a PWM control input, a PWM output and an inverted PWM output;

a high-side switch having a first terminal coupled to the DC voltage input, a second terminal coupled to the regulator output and a control input coupled to the PWM output;

a low-side switch having a first terminal coupled to ground, a second terminal coupled to the regulator output and a control input coupled to the inverted PWM output; and

a comparator having an inverting input coupled to the power supply output, a non-inverting input coupled to a reference voltage and an output coupled to the PWM control input.

11. A switching power supply having noise suppression capabilities, comprising:

a switching regulator having a direct current (DC) voltage input, an oscillator input and an output;

a filter having a first end coupled to the output of the switching regulator and a second end providing an output for the power supply;

a variable-frequency oscillator coupled to the oscillator input of the switching regulator, said variable-frequency oscillator having a frequency control input and an output that provides a variable-frequency oscillating signal;

a pseudorandom number generator that provides a pseudorandom sequence of digital bits;

a digital-to-analog converter configured to accept the pseudorandom sequence of digital bits and provide a control signal having a variable voltage; and

a voltage controlled oscillator having a frequency control input configured to accept the control signal and an output that provides the variable-frequency oscillating signal.

12. The switching power supply of claim 11 wherein the filter comprises:

an inductor having a first end coupled to the output of the switching regulator and a second end providing the output of the power supply; and

a capacitor having a first end coupled to the second end of the inductor and a second end coupled to ground.

13. The switching power supply of claim 11 wherein the switching regulator and the variable-frequency oscillator comprise an integrated circuit.

14. The switching power supply of claim 11 wherein the switching regulator comprises:

a pulse width modulator (PWM) having a PWM oscillating signal input configured to accept the variable-frequency oscillating signal, a PWM control input, a PWM output and an inverted PWM output;

a high-side switch having a first terminal coupled to the DC voltage input, a second terminal coupled to the regulator output and a control input coupled to the PWM output;

a low-side switch having a first terminal coupled to ground, a second terminal coupled to the regulator output and a control input coupled to the inverted PWM output; and

a comparator having an inverting input coupled to the power supply output, a non-inverting input coupled to a reference voltage and an output coupled to the PWM control input.

15. A switching power supply having reduced switching noise, comprising:

switching regulator means for converting a direct current (DC) input voltage to an DC output voltage; and

a variable-frequency oscillating means coupled to the switching regulator means for varying a rate at which the regulator means switches when the DC input voltage is being converted to the DC output voltage.

16. The switching power supply of claim 15 wherein the variable-frequency oscillating means comprises a voltage controlled operator means for providing an oscillating signal having a frequency dependent upon the voltage of a control signal.

17. The switching power supply of claim 16 wherein the control signal comprises a digital-to-analog converted pseudorandom sequence of digital bits.

18. The switching power supply of claim 16 wherein the variable-frequency oscillating means further comprises an alternating waveform generator means.

19. A method of reducing noise in a switching power supply, comprising the steps of:

converting a direct current (DC) input voltage to a DC output voltage using a switching power supply;

varying the rate at which the switching power supply switches during the step of converting.

20. The method of claim 19 wherein the step of varying comprises a step of varying a voltage level of a control signal at a control input of a voltage controlled oscillator (VCO) to provide a pulse width modulator oscillating signal determinative of the rate of switching.

21. The method of claim 20 wherein the step of varying the voltage level of the VCO comprises providing a digital-to-analog converted sequence of pseudorandom bits to the control input of the VCO.

22. The method of claim 20 wherein the step of varying the voltage level of the VCO comprises providing an alternating voltage signal to the control input of the VCO.