Redriver with Output Receiver Detection that Mirrors Detected Termination on Output to Input

• US 20120235704A1
• Filed: 06/01/2012
• Published: 09/20/2012
• Est. Priority Date: 10/23/2008
• Status: Active Grant

• Current Assignee: Diodes Incorporated
• Original Assignee: Pericom Semiconductor Corporation (Diodes Incorporated)
• Inventors: Yeung, Tony, Zhang, Michael Y.
• Granted Patent: US 8,610,463 B2
• Time in Patent Office: Days
• US Class Current: 326/30
• CPC Class Codes: H03K 19/0005 Modifications of input or output impedance
• CPC Class Codes: H04B 3/36 Repeater circuits H04B3/58 takes precedence
• CPC Class Codes: H04L 25/0272 Arrangements for coupling to multiple lines, e.g. for differential transmission
• CPC Class Codes: H04L 25/0278 Arrangements for impedance matching
• CPC Class Codes: H04L 25/0286 Provision of wave shaping within the driver wave shaping per se H04L25/03834
• CPC Class Codes: H04L 25/029 Provision of high-impedance states
• CPC Class Codes: H04L 25/0298 Arrangement for terminating transmission lines
• CPC Class Codes: H04L 25/03878 Line equalisers; line build-out devices

Abstract

A redriver chip is inserted between a transmitter chip and a receiver chip and re-drives differential signals from the transmitter chip to the receiver chip. The redriver chip has switched output termination that switches to a high value to detect far-end termination at the receiver chip, and to a low value for signaling. An output detector detects when the receiver chip has termination to ground and enables switched input termination to provide termination to ground on the lines back to the transmitter chip so that the far-end termination on the receiver chip is mirrored back to the transmitter chip, hiding the redriver chip. An input signal detector detects when the transmitter chip begins signaling and enables an equalizer, limiter, pre-driver, and output stage to re-drive the signals to the receiver chip. The input signal detector also causes the switched output termination to switch to the low value termination for signaling.

Claims

1. A re-detecting redriver device comprising:

a differential input including a true differential input and a complement differential input;

a differential output including a true differential output and a complement differential output, the true and complement differential outputs configured to being driven to opposite states by the redriver device when transmitting data;

a differential circuit, coupled to the differential input, for buffering data received onto the differential output as re-transmitted data; and

an impedance minor circuit, coupled to the differential input, for detecting an upstream termination on the differential input and for controlling a termination on the true differential output and on the complement differential output to reflect the upstream termination detected on the differential input, wherein the upstream termination is re-detected after a period of time has elapsed,

whereby the upstream termination is mirrored to the differential output in response to the upstream termination detected on the differential input.

2. The re-detecting redriver device of claim 1 wherein the impedance mirror circuit further comprises:

an input signal detector, coupled to the differential input, for activating a signal-detect signal when the true differential input and the complement differential input are varying in voltage in response to the data received;

a true switched output termination resistor, coupled to the true differential output in response to the signal-detect signal being activated, and disconnected from the true differential output in response to the signal-detect signal not being activated; and

a complement switched output termination resistor, coupled to the complement differential output in response to the signal-detect signal being activated, and disconnected from the complement differential output in response to the signal-detect signal not being activated,

whereby output termination is switched to the differential output in response to the signal-detect signal from the input signal detector.

3. The re-detecting redriver device of claim 2 further comprising:

a first coupling capacitor coupled to the true line of the differential output; and

a second coupling capacitor coupled to the complement line of the differential output.

4. The re-detecting redriver device of claim 2 further comprising:

an output detector, coupled to the differential output, for sensing a termination impedance on the differential output and activating a detect signal in response to the termination impedance detected.

5. The re-detecting redriver device of claim 4 further comprising:

a true switched input termination resistor, coupled to the true differential input in response to the detect signal being activated, and disconnected from the true differential input in response to the detect signal not being activated; and

a complement switched input termination resistor, coupled to the complement differential input in response to the detect signal being activated, and disconnected from the complement differential input in response to the detect signal not being activated;

wherein the true switched input termination resistor and the complement switched input termination resistor provide termination when the output detector detects the termination impedance,

whereby the termination impedance is mirrored to the differential input by the true switched input termination resistor and the complement switched input termination resistor on the differential input of the redriver device.

6. The re-detecting redriver device of claim 5 further comprising:

a true input termination transistor, coupled in series with the true switched input termination resistor, for blocking current flow through the true switched input termination resistor when the detect signal is not activated, and for conducting current through the true switched input termination resistor when the detect signal is activated; and

a complement input termination transistor, coupled in series with the complement switched input termination resistor, for blocking current flow through the complement switched input termination resistor when the detect signal is not activated, and for conducting current through the complement switched input termination resistor when the detect signal is activated.

7. The re-detecting redriver device of claim 6 wherein the true input termination transistor and the true switched input termination resistor are connected in series to the true differential input;

wherein the complement input termination transistor and the complement switched input termination resistor are connected in series to the complement differential input.

8. The re-detecting redriver device of claim 2 wherein the differential redriving circuit further comprises:

an equalizer that shapes a waveform of the data received over the differential input to generate equalized data;

a pre-driver that receives the equalized data from the equalizer and generates buffered data; and

an output stage that receives the buffered data from the pre-driver and drives current onto the true differential output and onto the complement differential output.

9. The re-detecting redriver device of claim 4 wherein the output detector detects a D.C. voltage on the differential output that depends on a charging time of the first coupling capacitor;

wherein the charging time is greater when the termination impedance detected on the output is enabled than when the termination impedance is not enabled.

10. The re-detecting redriver device of claim 8 wherein the output detector further comprises:

a pulse generator that generates a pulse;

a delay circuit that generates a delayed pulse;

a true compare gate that receives the true differential output and generates a true detect signal when the true differential output is below a compare voltage;

a complement compare gate that receives the complement differential output and generates a complement detect signal when the complement differential output is below a compare voltage;

a combining gate that combines the true detect signal and the complement detect signal to generate a combined detect signal; and

a flip-flop that receives the delayed pulse as a clock, and samples the combined detect signal in response to the delayed pulse to generate the detect signal.

11. The re-detecting redriver device of claim 10 wherein the pulse generator is activated by a reset signal or detection of power being applied to the redriver device.

12. The re-detecting redriver device of claim 10 further comprising:

a true switched output-sensing termination resistor, coupled to the true differential output in response to an evaluation signal being activated, and disconnected from the true differential output in response to the evaluation signal not being activated;

a complement switched output-sensing termination resistor, coupled to the complement differential output in response to the evaluation signal being activated, and disconnected from the complement differential output in response to the evaluation signal not being activated;

wherein the evaluation signal is activated when the output detector detects the termination impedance.

13. A method for operating a redriver to minor a termination impedance to an input comprising:

connecting a first output termination resistance to an output to set an output impedance to a low-impedance state;

waiting for a measuring period of time to elapse after connecting the first output termination resistance to the output;

sensing the output to detect when the termination impedance is connected; and

when connection of the termination impedance is detected, connecting an input termination resistance to an input to minor the termination impedance;

wherein an input impedance is set to the low-impedance state to minor the termination impedance.

14. The method of claim 13 further comprising:

repeating detection of the termination impedance to re-detect the termination impedance after a re-detect period of time has elapsed, and switching the input termination resistance to the input to minor the termination impedance,

whereby termination detection is repeated after the re-detect period of time.

15. The method of claim 13 further comprising:

continuously repeating detection of the termination impedance to re-detect the termination impedance after each re-detect period of time has elapsed,

whereby termination detection is continuously repeated after each re-detect period of time.

16. The method of claim 13 further comprising:

sensing the input to detect when the transmitter is varying the input to send transmission signals and activating an input-sensed signal when detected;

when the input-sensed signal is activated, connecting a second output termination resistance to the output and redriving the transmission signals received by the input to the output for re-transmission to set the output impedance to a second low-impedance state.

17. The method of claim 16 further comprising:

when the input-sensed signal is activated, disconnecting the first output termination resistance to the output for replacement by the second output termination resistance;

wherein the second low-impedance state has a higher impedance than the low-impedance state, wherein impedance is lowered when the input-sensed signal is activated.

18. A re-detecting redriver device comprising:

a differential input including a true differential input and a complement differential input;

a differential output including a true differential output and a complement differential output, the true and complement differential outputs configured to being driven to opposite states by the redriver device when transmitting data;

a differential circuit, coupled to the differential input, for buffering data received to the differential output as re-transmitted data; and

an impedance minor circuit, coupled to the differential output, for detecting a termination impedance on the differential output and for controlling a termination on the true differential input and on the complement differential input to reflect the termination impedance detected on the differential output, wherein the termination impedance is re-detected after a period of time has elapsed,

whereby the termination impedance is mirrored to the differential input in response to the termination impedance detected on the differential output.

19. The re-detecting redriver device of claim 18 wherein the impedance mirror circuit further comprises:

an output detector, coupled to the differential output, for sensing a termination impedance on the differential output and activating a detect signal in response to detection of the termination impedance;

a true switched input termination resistor, coupled to the true differential input in response to the detect signal being activated, and disconnected from the true differential input in response to the detect signal not being activated; and

a complement switched input termination resistor, coupled to the complement differential input in response to the detect signal being activated, and disconnected from the complement differential input in response to the detect signal not being activated,

whereby input termination is switched to the differential input in response to the detect signal from the output detector.

20. The re-detecting redriver device of claim 19 further comprising:

a first coupling capacitor coupled to the true line of the differential input; and

a second coupling capacitor coupled to the complement line of the differential input.