Methods and structures to generate on/off keyed carrier signals for signal isolators

• US 9,660,848 B2
• Filed: 09/15/2014
• Issued: 05/23/2017
• Est. Priority Date: 09/15/2014
• Status: Active Grant

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Analog Devices Global Unlimited Company (Analog Devices, Inc.)
• Inventors: Chen, Baoxing, Yun, Ruida, Sun, Yuanjie
• Primary Examiner(s): Burd, Kevin M
• Application Number:
  US14/486,937
• Publication Number:
  US 20160080181A1
• Time in Patent Office: 981 Days
• Field of Search: 375295, 375312
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48137 the bodies being arranged next to each other, e.g. on a common substrate
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H03B 5/1215 the current source or degeneration circuit being in common to both transistors of the pair, e.g. a cross-coupled long-tailed pair
• CPC Class Codes: H03B 5/1228 the amplifier comprising one or more field effect transistors
• CPC Class Codes: H03C 1/60 with one sideband wholly or partially suppressed
• CPC Class Codes: H04L 25/0286 Provision of wave shaping within the driver wave shaping per se H04L25/03834
• CPC Class Codes: H04L 27/04 Modulator circuits; Transmitter circuits

Abstract

An oscillator for a signal isolator system includes a capacitor and an inductor connected in parallel, two pairs of cross-coupled switches and a control switch. The capacitor, the inductor and the cross-coupled switches form an oscillator. The control switch controls operation of the oscillator between an ON state and an OFF state in response to a data signal to be communicated across an isolation barrier. The inductor may be formed from a winding of an isolation transformer, which reduces component count as compared to a system that provides a separate inductor. Other embodiments may include a current-supplying kickstart circuit and a shorting transistor that can speed transition between the ON and OFF states.

Claims

1. A transmitter system for a signal isolator system, comprising:

an oscillator circuit coupled to an isolator device,

a control switch, coupled between the oscillator circuit and a constant voltage node, having an input for an input signal to be transmitted by the system; and

accelerating means for accelerating transition of the oscillator circuit on a transition between an ON state and an OFF state as determined by the input signal.

2. The system of claim 1, where the accelerating means includes a switch, coupled between two components of the oscillator, and configured to short circuit an LC circuit coupled to the oscillator circuit.

3. The system of claim 1, wherein the accelerating means includes a current injection circuit, coupled to the oscillator circuit, configured to couple a current source to an LC circuit coupled to the oscillator circuit.

4. A transmitter system for a signal isolator system, comprising:

an oscillator coupled to an isolator device,

a control switch, coupled between the oscillator and a constant voltage node, having an input for an input signal to be transmitted by the system; and

a quenching switch, coupled between two components of the oscillator, that becomes conductive during a transition from an ON state of the oscillator to an OFF state of the oscillator as determined by the input signal.

5. The transmitter system of claim 4, wherein the isolator device comprises a transformer, a first winding of which is an inductor of the oscillator.

6. The transmitter system of claim 4, wherein the isolator device comprises a capacitor.

7. The transmitter system of claim 4, wherein the oscillator comprises:

an inductor connected between first and second nodes;

a first pair of cross-coupled transistors, including;

a first transistor coupled between the first node and a first voltage supply and having a control input coupled to the second node, and

a second transistor coupled between the second node and the first voltage supply and having a control input coupled to the first node, and

a second pair of cross-coupled transistors, including;

a third transistor one coupled between the first node and a third node and having a control input coupled to the second node, and

a fourth transistor coupled between the second node and the third node and having a control input coupled to the first node.

8. The transmitter system of claim 4, wherein the oscillator comprises:

a capacitor connected between first and second nodes;

a pair of cross-coupled transistors, including;

a first transistor coupled between the first node and a first voltage supply and having a control input coupled to the second node, and

a second transistor coupled between the second node and the first voltage supply and having a control input coupled to the first node, and

a pair of inductors, including;

a first inductor coupled between the first node and a second voltage supply, and

a second inductor coupled between the second node and the second voltage supply.

9. The transmitter system of claim 4, further comprising a current injection circuit, coupled to the oscillator, and configured to become active during a transition from an OFF state of the oscillator to an ON state of the oscillator as determined by the input signal.

10. The transmitter system of claim 4, further comprising a voltage regulator coupled between the constant voltage node and the oscillator.

11. A transmitter system for a signal isolator system, comprising:

an oscillator coupled to an isolator device,

a control switch, coupled between the oscillator and a constant voltage node, having an input for an input signal to be transmitted by the system; and

a current injection circuit comprising a plurality of transistors and coupled to the oscillator, wherein at least one of the plurality of transistors is configured to become conductive during a transition from an OFF state of the oscillator to an ON state of the oscillator as determined by the input signal.

12. The transmitter system of claim 11, wherein the isolator device comprises a transformer, a first winding of which is an inductor of the oscillator.

13. The transmitter system of claim 11, wherein the isolator device comprises a capacitor.

14. The transmitter system of claim 11, further comprising a quenching switch, coupled between two capacitor plates, configured to become conductive during a transition from an ON state of the oscillator to an OFF state of the oscillator as determined by the input signal.

15. The transmitter system of claim 11, wherein the oscillator comprises:

an inductor connected between first and second nodes;

a first pair of cross-coupled transistors, including;

a first transistor coupled between the first node and a first voltage supply and having a control input coupled to the second node, and

a second transistor coupled between the second node and the first voltage supply and having a control input coupled to the first node, and

a second pair of cross-coupled transistors, including;

a third transistor coupled between the first node and a third node and having a control input coupled to the second node, and

a fourth transistor coupled between the second node and the third node and having a control input coupled to the first node.

16. The transmitter system of claim 11, wherein the oscillator comprises:

a capacitor connected between first and second nodes;

a pair of cross-coupled transistors, including;

a first transistor coupled between the first node and a first voltage supply and having a control input coupled to the second node, and

a second transistor coupled between the second node and the first voltage supply and having a control input coupled to the first node, and

a pair of inductors, including;

a first inductor coupled between the first node and a second voltage supply, and

a second inductor coupled between the second node and the second voltage supply.

17. The transmitter system of claim 11, further comprising a voltage regulator coupled between the constant voltage node and the oscillator.

18. A method of managing transitions in an ON-OFF signal isolation system, comprising:

selectively driving an oscillator from a first circuit path in response to an input signal to be transmitted across an isolation barrier, wherein the oscillator is driven to an ON state for one state of the input signal and is driven to an OFF state for another state of the input signal;

when the input signal transitions between an ON state and an OFF state, engaging a second circuit path, ancillary to the first circuit path, to alter an amount of current passing through the oscillator.

19. The method of claim 18, comprising, when the input signal changes state to cause the oscillator to transition from an OFF state to the ON state, injecting current into the oscillator from the second circuit path.

20. The method of claim 18, wherein, when the input signal changes state to cause the oscillator to transition from an ON state to the OFF state, the second circuit path is a shorting current path within the oscillator.

21. The method of claim 20, wherein the shorting current path remains active for an entire duration of the OFF state.

22. The method of claim 20, wherein the shorting current path remains active only for an initial portion of the OFF state.

23. The method of claim 19, further comprising terminating the current injection after a predetermined portion of the ON state has elapsed.

24. The method of claim 18, further comprising repeating the method for each of a plurality of transmission channels.

25. A multi-channel transmitter system for a signal isolator system, comprising:

a plurality of channels for transmission of respective signals across an isolation barrier, including first and second channels each comprising a transmitter and an isolator device,

wherein the transmitter of each of the first and second channels comprises;

an oscillator circuit coupled to the isolator device of the channel,

a control switch, coupled between the oscillator circuit and a constant voltage node, having an input for an input signal to be transmitted by the system; and

accelerating means for accelerating transition of the oscillator circuit on a transition between an ON state and an OFF state as determined by the input signal.

26. The system of claim 25, wherein the accelerating means is a current injection circuit, coupled to the oscillator circuit, configured to become active during a transition from an OFF state of the oscillator circuit to an ON state of the oscillator as determined by the input signal.

27. The system of claim 25, wherein the accelerating means is a quenching switch, coupled between two components of the oscillator circuit, configured to become conductive during a transition from an ON state of the oscillator circuit to an OFF state of the oscillator as determined by the input signal.

28. The system of claim 25, wherein the transmitters of the first and second channels each transmit their respective signals in a common direction across the isolation barrier.

29. The system of claim 25, wherein:

at least one transmitter transmits its respective signal in a first direction across the isolation barrier and

at least one other transmitter transmits its respective signal in a second direction across the isolation barrier, opposite the first direction.