Pseudo-differential interfacing device having a switching circuit

• US 7,884,648 B2
• Filed: 05/20/2008
• Issued: 02/08/2011
• Est. Priority Date: 07/09/2007
• Status: Expired due to Fees

• Current Assignee: Zxnoise, LLC
• Original Assignee: Excem SAS
• Inventors: Broyde, Frédéric, Clavelier, Evelyne
• Primary Examiner(s): Barnie; Rexford N
• Assistant Examiner(s): Tran; Thienvu V
• Application Number:
  US12/599,114
• Publication Number:
  US 20100213971A1
• Time in Patent Office: 994 Days
• Field of Search: 326/30, 326 82- 87
• US Class Current: 326/86
• CPC Class Codes: H04L 25/0276 Arrangements for coupling common mode signals
• CPC Class Codes: H04L 25/085 Arrangements for reducing interference in line transmission systems, e.g. by differential transmission

Abstract

The invention relates to an interfacing device for pseudo-differential transmission through interconnections used for sending a plurality of electrical signals. The interfacing device of the invention includes signal terminals and a common terminal. A transmitting circuit receives the input signals of the transmitting circuit coming from a source. The output of the transmitting circuit delivers, when the transmitting circuit is in the activated state, voltages between one of the signal terminals and the reference terminal (ground). A receiving circuit delivers, when the receiving circuit is in the activated state, output signals of the receiving circuit determined each by the voltage between one of the signal terminals and the common terminal, to the destination. In the closed state, the common terminal switching circuit is, for the common terminal, equivalent to a voltage source delivering a constant voltage, connected in series with a passive two-terminal circuit element presenting a low impedance.

Claims

1. A device for transmitting signals through a plurality of transmission channels, in a known frequency band, comprising:

m signal terminals, a common terminal and a reference terminal, the signal terminals and the common terminal being configured to be connected to an interconnection having at least m+1 conductors, m being an integer greater than or equal to 2;

a receiving circuit delivering, when the receiving circuit is in the activated state, p output signals of the receiving circuit corresponding each to a transmission channel, p being an integer greater than or equal to 1 and less than or equal to m, the input of the receiving circuit being coupled to at least p of the signal terminals and to the common terminal, each of the output signals of the receiving circuit being mainly determined by the voltage between one and only one of the signal terminals and the common terminal;

a transmitting circuit receiving q input signals of the transmitting circuit corresponding each to a transmission channel, q being an integer greater than or equal to 2 and less than or equal to m, the output of the transmitting circuit being coupled to at least q of the signal terminals, the output of the transmitting circuit delivering, when the transmitting circuit is in the activated state, q transmission variables, each transmission variable being either a voltage between one of the signal terminals and the reference terminal or a current flowing out of one of the signal terminals, each transmission variable being mainly determined by one and only one of the input signals of the transmitting circuit; and

a common terminal switching circuit having an open state and a closed state, the common terminal switching circuit having a return current terminal connected to the common terminal, the common terminal switching circuit being in the closed state when the transmitting circuit is in the activated state, the common terminal switching circuit being in the open state when the receiving circuit is in the activated state, the common terminal switching circuit in the closed state providing, between the common terminal and the reference terminal, a voltage approximately equal to the sum of a constant voltage and of the voltage, determined using the active sign convention, which would appear across a first passive two-terminal circuit element subject to the current flowing from the return current terminal to the common terminal.

2. The device of claim 1, wherein the common terminal switching circuit in the open state provides a current flowing from the return current terminal to the common terminal approximately equal to the sum of a constant current and of the current flowing out of a second passive two-terminal circuit element subject to the voltage between the common terminal and the reference terminal, and wherein the product of the absolute value of the small-signal impedance of the first passive two-terminal circuit element, at a first quiescent operating point, by the absolute value of the small-signal admittance of the second passive two-terminal circuit element, at a second quiescent operating point, is, in at least a part of the known frequency band, less than or equal to ½

.

3. The device of claim 1, wherein the common terminal switching circuit in the closed state is such that, at the first quiescent operating point, the first passive two-terminal circuit element has a small-signal impedance having, in the known frequency band, an absolute value less than or equal to three hundred ohms.

4. The device of claim 1, wherein the relationship between the current flowing out of the return current terminal and the voltage between the common terminal and the reference terminal is linear when the common terminal switching circuit is in the closed state and/or when the common terminal switching circuit is in the open state.

5. The device of claim 1, wherein the small-signal impedance of the first passive two-terminal circuit element can be adjusted by electrical means.

6. The device of claim 2, wherein the small-signal admittance of the second passive two-terminal circuit element can be adjusted by electrical means.

7. The device of claim 1, wherein the device constitutes a part of an integrated circuit, the interconnection being realized inside the integrated circuit.

8. The device of claim 1, wherein the device constitutes a part of an integrated circuit, each of the m signal terminals being coupled to one or more pins of the integrated circuit, the common terminal being coupled to one or more pins of the integrated circuit.

9. The device of claim 1, further comprising a termination circuit coupled to each of the signal terminals and to the common terminal, the termination circuit being, when the termination circuit is in the activated state, for the signal terminals and the common terminal, approximately equivalent to a network consisting of m branches, each of the branches having a first terminal and a second terminal, each of the branches consisting of a passive linear two-terminal circuit element connected in series with a voltage source delivering a constant voltage, the first terminal of each of the branches being connected to one and only one of the signal terminals, the second terminal of each of the branches being connected to the common terminal, each of the signal terminals being connected to the first terminal of one and only one of the branches.

10. The device of claim 9, wherein the impedance matrix, with respect to the common terminal, of the termination circuit in the activated state can be adjusted by electrical means.

11. The device of claim 9, wherein the termination circuit has an activated state and a deactivated state, each current flowing from the termination circuit to one of the signal terminals being substantially zero when the termination circuit is in the deactivated state.