Spread spectrum modulation technique for isolation devices

Patent metadata

Field	Value
Publication number	US-2023378624-A1
Application number	US-202217750659-A
Country	US
Kind code	A1
Filing date	May 23, 2022
Priority date	May 23, 2022
Publication date	Nov 23, 2023
Grant date	—

Abstract

A device includes a transformer having primary windings and secondary windings, and a transmit circuit coupled to the primary windings. The transmit circuit is configured to receive an input signal, and provide a carrier signal to the primary windings responsive to the input signal. The device also includes a receive circuit coupled to the secondary windings. The receive circuit is configured to receive the carrier signal from the secondary windings, and provide an output signal responsive to the carrier signal. The receive circuit includes a variable capacitor coupled in parallel to the secondary windings, and a spread spectrum modulation circuit configured to modulate a capacitance of the variable capacitor.

First claim

What is claimed is:

1 . A device, comprising:
a transformer having primary windings and secondary windings; a transmit circuit coupled to the primary windings and configured to:
receive an input signal; and
provide a carrier signal to the primary windings responsive to the input signal; and
a receive circuit coupled to the secondary windings and configured to:
receive the carrier signal from the secondary windings; and
provide an output signal responsive to the carrier signal;
wherein the receive circuit includes:
a variable capacitor coupled in parallel to the secondary windings; and
a spread spectrum modulation circuit configured to modulate a capacitance of the variable capacitor.

2 . The device of claim 1 , wherein the transmit circuit does not include a power supply pin and is configured not to be coupled to a power supply, and wherein the receive circuit is configured to be coupled to a power supply.

3 . The device of claim 2 , wherein a frequency of the carrier signal is modulated responsive to the capacitance of the variable capacitor being modulated.

4 . The device of claim 2 , wherein the transmit circuit is configured to provide the carrier signal responsive to the input signal according to an on-off keying modulation scheme.

5 . The device of claim 1 , wherein the spread spectrum modulation circuit includes:
an oscillator configured to provide a clock signal; and a digital logic circuit configured to:
receive the clock signal from the oscillator; and
provide a capacitor control signal responsive to the clock signal, wherein the capacitor control signal is configured to modulate the capacitance of the variable capacitor.

6 . The device of claim 5 , wherein the digital logic circuit is configured to modulate the capacitance of the variable capacitor in a stairstep manner as a function of time.

7 . The device of claim 1 , wherein the variable capacitor includes:
a first series combination of a first capacitor and a first transistor; and a second series combination of a second capacitor and a second transistor, wherein the first series combination, the second series combination, and the secondary windings are in parallel; wherein the spread spectrum modulation circuit is configured to control the first and second transistors to modulate the capacitance.

8 . The device of claim 1 , wherein the secondary windings include a center tap that divides the secondary windings into a first portion and a second portion, and wherein the variable capacitor includes:
a first series combination of a first capacitor and a first transistor; a second series combination of a second capacitor and a second transistor, wherein the first series combination, the second series combination, and the first portion of the secondary windings are in parallel; a third series combination of a third capacitor and a third transistor; and a fourth series combination of a fourth capacitor and a fourth transistor, wherein the third series combination, the fourth series combination, and the second portion of the secondary windings are in parallel; wherein the spread spectrum modulation circuit is configured to control the first and third transistors together, and the second and fourth transistors together, to modulate the capacitance.

9 . The device of claim 8 , wherein the primary windings include a center tap and provide the carrier signal to the secondary windings as a differential carrier signal.

10 . An isolation device, comprising:
a transmit circuit; an isolation barrier coupled to the transmit circuit; and a receive circuit coupled to the isolation barrier; wherein the transmit circuit is configured to provide a carrier signal to the receive circuit; and wherein the receive circuit is configured to modulate a frequency of the carrier signal.

11 . The isolation device of claim 10 , wherein the transmit circuit is configured to provide the carrier signal to the receive circuit across the isolation barrier responsive to an input signal, and wherein the receive circuit is configured to provide an output signal responsive to the received carrier signal across the isolation barrier.

12 . The isolation device of claim 11 , wherein the transmit circuit is configured to provide the carrier signal responsive to the input signal according to an on-off keying modulation scheme.

13 . The isolation device of claim 10 , wherein the transmit circuit does not include a power supply pin and is configured not to be coupled to a power supply, and wherein the receive circuit is configured to be coupled to a power supply.

14 . The isolation device of claim 10 , further comprising a variable capacitor coupled to the receive circuit, wherein the receive circuit is configured to modulate the capacitance of the variable capacitor to modulate the frequency of the carrier signal.

15 . The isolation device of claim 14 , wherein the receive circuit is configured to modulate the capacitance of the variable capacitor in a stairstep manner, a triangle manner, or a sawtooth manner as a function of time.

16 . The isolation device of claim 14 , wherein the variable capacitor includes:
a first series combination of a first capacitor and a first transistor; and a second series combination of a second capacitor and a second transistor, wherein the first series combination, the second series combination, and an element of the isolation barrier are in parallel; and wherein the receive circuit is configured to control the first and second transistors to modulate the capacitance.

17 . The isolation device of claim 10 , wherein the transmit circuit is configured to provide the carrier signal to the receive circuit as a differential carrier signal.

18 . A receive circuit operable to be coupled to secondary windings of an isolation transformer, the isolation transformer includes primary windings coupled to transmit circuitry and the receive circuit comprising:
a receiver coupled to the secondary windings; a first series combination of a first capacitor and a first transistor; a second series combination of a second capacitor and a second transistor, wherein the first series combination, the second series combination, the receiver and the secondary windings are coupled in parallel; and a spread spectrum modulation circuit having a first output coupled to a control terminal of the first transistor and having a second output coupled to a control terminal of the second transistor.

19 . The receive circuit of claim 19 , wherein the transmit circuitry is operable to transmit a carrier signal having a carrier frequency and the carrier frequency is modulated responsive to turning on/off the first transistor, the second transistor, or both the first transistor and the second transistor.

20 . The receive circuit of claim 19 , wherein the receiver is configured to receive the carrier signal as a differential carrier signal.

Assignees

• Texas Instruments Inc

Inventors

• Nasum Sreeram Subramanyam
• Barot Kashyap

Classifications

• H01P1/36 Primary

  Isolators · CPC title

• H04B1/69 Primary

  Spread spectrum techniques · CPC title

• H04B1/16

  Circuits · CPC title

• H01F27/28 Primary

  Coils; Windings; Conductive connections · CPC title

• H04L27/04

  Modulator circuits; Transmitter circuits · CPC title