CN113949419A

CN113949419A - Novel automatic zero-stabilizing direct-current coupling receiver

Info

Publication number: CN113949419A
Application number: CN202111026801.1A
Authority: CN
Inventors: 杨波
Original assignee: Guangzhou Changyuxing Information Technology Co ltd
Current assignee: Guangzhou Changyuxing Information Technology Co ltd
Priority date: 2021-09-02
Filing date: 2021-09-02
Publication date: 2022-01-18

Abstract

The invention relates to the technical field of receivers, in particular to a novel automatic zero-stabilizing direct-current coupling receiver which comprises a positive input end, a negative input end, a first T-shaped coil, a second T-shaped coil, a resistor string and an equalizer, wherein the positive input end is connected with the input end of the first T-shaped coil, the negative input end is connected with the input end of the second T-shaped coil, the output end of the first T-shaped coil and the output end of the second T-shaped coil are connected in series with the resistor string, a first isolating switch is connected to the central node of the first T-shaped coil in front of the positive input end of the equalizer, a second isolating switch is connected to the central node of the second T-shaped coil in front of the negative input end of the equalizer, and a third isolating switch is connected between the positive input end and the negative input end of the equalizer. The invention can not conflict with the transmitting terminal in the automatic return-to-zero mode, can not influence the signal bandwidth, and can provide good input matching and good loop loss.

Description

Novel automatic zero-stabilizing direct-current coupling receiver

Technical Field

The invention relates to the technical field of receivers, in particular to a novel automatic zero-stabilizing direct-current coupling receiver.

Background

A conventional high speed serial/anti-serial (SERDES) Receiver (RX)) front end with T-coil is shown in fig. 1. The main module has a T-shaped coil, a matching resistor string Rterm and a Continuous Time Linear Equalizer (CTLE). Typically, a fully differential version is used to minimize common noise, such as noise from the power supply. Therefore, the positive electrode and the negative electrode are symmetrical.

The input is first applied to the T-coil. For the positive input, the T-coil consists of two inductors (e.g., Lp1 and Lp 2). The purpose of these two inductors is to work with a matching resistor string Rterm (termination resistor Rp), provide a 50 ohm impedance to the outside world, and extend the bandwidth to minimize signal loss. Usually the input also needs to be connected to a pair of large ESD diodes for ESD protection. However, these ESD diodes create a large parasitic load on the input terminal, greatly reducing the bandwidth of the input signal. The key advantage of the T-coil is that the center node is not sensitive to capacitive loads, and the conventional approach is to place an ESD diode at the center node to increase the input bandwidth. For clarity, the ESD diode is drawn as a capacitor as CESDP and placed in node ESDP. The output of the T-coil is fed to the next stage CTLE as the first gain block, which is crucial to have the smallest input reference offset, since this offset will be amplified by the CTLE and subsequent gain blocks and cause system errors. In an actual silicon chip, the input reference bias voltage of the CTLE varies from several mV to tens of mV due to device characteristic mismatch caused by layout parasitic effect, non-uniform doping, mismatch of a lithographic circuit board PCB, and the like. The bias voltage VOFFSET is a voltage source at the CTLE input as shown in fig. 2.

This offset can be corrected by using auto-zero techniques or offset cancellation. However, in both of these ways we need a method to short the input of the CTLE, as shown in fig. 3. If we turn off the auto-zero switch as shown in fig. 3, the inputs of both CTLEs will be forced to be equal, CTLEINP ═ CTLEINN. The CTLE differential input is effectively zero. Thus, the output of the CTLE will be the input reference offset of the CTLE multiplied by the gain of the CTLE. The output voltage may be digitized by a DAC or stored in a capacitor for digital or analog cancellation. Since we know the CTLE gain, the system also knows the input reference offset.

However, one disadvantage of the architecture in fig. 3 is that INP and INN will be shorted together. Since this is a DC coupled receiver, i.e. there is no ac coupling capacitance separating the DC of the transmitting end (TX) and the Receiver (RX). We need two switches to separate CTLEINP and INP, and CTLEINN and INN. Without these two switches CTLEINP/CTLEINN would collide with the external input voltage INP/INN, resulting in CTLEINP not being equal to CTLEINN, and CTLE would effectively see a non-zero input, with the auto-zero output being erroneous. As a remedy, fig. 4 uses a solution with three auto-zero switches. In auto-zero mode, AZ SW1P and AZ SW1N are on, while AZ SW2 is off. Since INP is not separated by CTLEINP's switch (the same applies to INN and CTLEINN), CTLE auto-zero switch does not have the collision problem of the transmit side (TX). In the task or operation mode as shown in fig. 5, AZ SW1P and AZ SW1N are turned off and AZ SW2 is turned on, so that the normal input voltage VIN is shifted to the CTLE input and the CTLE output is signal + offset amplified.

However, this approach has its own drawbacks. The on-resistances of AZ SW1P and AZ SW1N and matching resistor string Rterm are in series in the signal path of AZ SW1P and AZ SW 1N. The on-resistance of the switch also varies with the rotation angle and swing. Thus, the total input resistance will be a variable switch on resistance plus a fixed multi-resistance. Changes in input impedance can cause reflections of the signal, affecting system performance. In addition, the switch on-resistance is that after the T-shaped coil and the on-resistance reach the peak value, because we can not adjust the signal bandwidth of the switch to be large, otherwise, parasitic load can be generated, so that the impedances CTLEINP and CTLEINN are not the impedance which is provided by the matching resistor string Rterm and is 50 ohms, but the impedance which is provided by the matching resistor string Rterm + capacitor and the input return loss is reduced, are provided by the input.

Disclosure of Invention

In order to overcome the above-mentioned drawbacks of the prior art, the present invention provides a novel dc-coupled receiver with auto-zero stabilization, so as to solve the above-mentioned problems in the background art.

The technical scheme adopted by the invention for solving the problems in the prior art is as follows: the utility model provides an automatic novel direct current coupling receiver of steady zero, includes positive input, negative input, first T type coil, second T type coil, resistor string and balanced device, the input of first T type coil is connected to the positive input, the input of second T type coil is connected to the negative input, the output of first T type coil and the output series connection of second T type coil the resistor string, on the central node of first T type coil with be connected with first isolator before the positive input of balanced device, on the central node of second T type coil with be connected with the second before the negative input of balanced device and return isolator, still be connected with the third isolator between the positive input of balanced device and the negative input.

In a preferred embodiment of the present invention, a first diode is connected to a center node of the first T-shaped coil, and a second diode is connected to a center node of the second T-shaped coil.

As a preferred aspect of the present invention, the first T-type coil includes a first inductor and a second inductor connected in series, the second T-type coil includes a third inductor and a fourth inductor connected in series, the first isolation switch and the first diode are connected to a central node of the first inductor and a central node of the second inductor, and the second isolation switch and the second diode are connected to a central node of the third inductor and a central node of the fourth inductor.

As a preferable aspect of the present invention, the resistor string includes two first resistors, a second resistor, and a third diode connected in series, and a connection node of the first resistor and the second resistor is connected to the third diode.

As a preferable aspect of the present invention, the first diode and the second diode are SDP diodes, and the third diode is a normal diode.

Compared with the prior art, the invention has the following technical effects:

1. according to the novel automatic zero-stabilizing direct-current coupling receiver, the first isolating switch and the second return isolating switch are arranged to isolate the input of the transmitting end and the linear equalizer, so that the receiver does not conflict with the transmitting end in an automatic zero-stabilizing mode;

2. the first isolating switch and the second isolating switch are larger, and the on-resistance is smaller. However, since they are connected to nodes (ESDP/ESDN) that are insensitive to parasitic capacitive loads, the relatively large parasitic loads (due to the large size) do not affect the signal bandwidth;

3. the input is connected in series with the T-coil using a pure 50 ohm matching resistor string Rterm (without parasitic load from the switch), so it provides good input matching and good loop loss.

Drawings

FIG. 1 is a schematic circuit diagram of a first prior art in a novel auto-zero stabilizing DC-coupled receiver according to the present invention;

FIG. 2 is a second schematic circuit diagram of a first prior art DC-coupled receiver with auto-zero stabilization according to the present invention;

FIG. 3 is a schematic circuit diagram of a second prior art in a novel auto-zero stabilizing DC-coupled receiver according to the present invention;

FIG. 4 is one of the schematic circuit diagrams of the third prior art in the novel auto-zero stabilizing DC-coupled receiver of the present invention;

FIG. 5 is a second schematic circuit diagram of a third prior art in a novel auto-zero stabilized DC-coupled receiver according to the present invention;

FIG. 6 is one of the schematic circuit diagrams of a novel auto-zero stabilized DC-coupled receiver of the present invention;

fig. 7 is a second schematic circuit diagram of a novel auto-zero stabilized dc-coupled receiver according to the present invention.

Reference numbers in the figures: 1. a positive input end; 2. a negative input terminal; 3. a first T-shaped coil; 4. a second T-shaped coil; 5. a resistor string; 6. an equalizer; 7. a first diode; 8. a second diode; 9. a first isolation switch; 10. a second isolation switch; 11. a third isolating switch; 31. a first inductor; 32. a second inductor; 41. a third inductor; 42. a fourth inductor; 51. a first resistor; 52. a second resistor; 53. and a third diode.

Detailed Description

The following further describes embodiments of the present invention with reference to the drawings. It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

As shown in fig. 6 and 7: the utility model provides an automatic novel direct current coupling receiver of steady zero, includes positive input 1, negative input 2, first T type coil 3, second T type coil 4, resistor string 5 and equalizer 6, positive input 1 connects the input of first T type coil 3, the input of second T type coil 4 is connected to negative input 2, the output of first T type coil 3 and the output of second T type coil 4 are established ties resistor string 5, on the central node of first T type coil 3 with be connected with first isolator 9 before the positive input 1 of equalizer 6, on the central node of second T type coil 4 with be connected with the second before the negative input 2 of equalizer 6 and return isolator, still be connected with third isolator 11 between positive input 1 of equalizer 6 and the negative input 2.

Preferably, a first diode 7 is connected to a central node of the first T-shaped coil 3, and a second diode 8 is connected to a central node of the second T-shaped coil 4.

Preferably, the first T-type coil 3 includes two first inductors 31 and two second inductors 32 connected in series, the second T-type coil 4 includes two third inductors 41 and two fourth inductors 42 connected in series, the first isolation switch 9 and the first diode 7 are connected to a central node of the first inductors 31 and the second inductors 32, and the second isolation switch and the second diode 8 are connected to a central node of the third inductors 41 and the fourth inductors 42.

Preferably, the resistor string 5 includes two first resistors 51, second resistors 52 and third diodes 53 connected in series, and a connection node of the first resistor 51 and the second resistor 52 is connected to the third diode 53.

Preferably, the first diode 7 and the second diode 8 are SDP diodes, and the third diode 53 is a normal diode.

The working principle is as follows: since the center node (ESDP/ESDN) of the T-coil can bear a large capacitive load, the first 9 and second 10 isolation switches can be amplified to minimize the on-resistance of the switches and increase the signal bandwidth.

In the auto-zero mode, the first and

second disconnectors

9, 10 are open and the third disconnector 11 is closed. Thus, the equalizer 6 can effectively see a zero differential input and can measure/store the offset voltage. Meanwhile, since it is separated from the equalizer 6 by closing the first and second isolation switches 9 and 10, and the third isolation switch 11 can be small in size since it does not need to contend with other sources, it is possible to use a minimum size and reduce a parasitic load on the input node of the equalizer 6 in practice.

In the mission mode, the first and second isolation switches 9 and 10 are closed, the third isolation switch 11 is opened, and signals are transmitted from the first and second isolation switches 9 and 10 to the equalizer 6 input.

Compared with the prior art, the invention has the following technical effects:

1. according to the novel automatic zero-stabilizing direct-current coupling receiver, the first isolating switch 9 and the second return isolating switch are arranged to isolate the input of the transmitting end and the linear equalizer 6, so that the receiver does not conflict with the transmitting end in an automatic zero-stabilizing mode;

2. the first isolating switch 9 and the second isolating switch are larger, and the on-resistance is smaller. However, since they are connected to nodes (ESDP/ESDN) that are insensitive to parasitic capacitive loads, the relatively large parasitic loads (due to the large size) do not affect the signal bandwidth;

3. the input terminal is connected in series with the T-type coil using a pure 50 ohm matching resistor string 5Rterm (without parasitic load from the switch), so it provides good input matching and good loop loss.

Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The utility model provides an automatic novel direct current coupling receiver of steady zero, includes positive input, negative input, first T type coil, second T type coil, resistor string and balanced device, the input of first T type coil is connected to positive input, the input of second T type coil is connected to the negative input, the output of first T type coil and the output series connection of second T type coil the resistor string, its characterized in that: a first isolating switch is connected to a center node of the first T-shaped coil and in front of the positive input end of the equalizer, a second isolating switch is connected to a center node of the second T-shaped coil and in front of the negative input end of the equalizer, and a third isolating switch is further connected between the positive input end and the negative input end of the equalizer.

2. The novel automatic zero-stabilizing direct-current coupling receiver according to claim 1, characterized in that: the center node of the first T-shaped coil is connected with a first diode, and the center node of the second T-shaped coil is connected with a second diode.

3. The novel automatic zero-stabilizing direct-current coupling receiver according to claim 2, characterized in that: the first T-shaped coil comprises a first inductor and a second inductor which are connected in series, the second T-shaped coil comprises a third inductor and a fourth inductor which are connected in series, the first isolating switch and the first diode are connected to the central nodes of the first inductor and the second inductor, and the second isolating switch and the second diode are connected to the central nodes of the third inductor and the fourth inductor.

4. The novel automatic zero-stabilizing direct-current coupling receiver according to claim 1, characterized in that: the resistor string comprises a first resistor, a second resistor and a third diode which are connected in series, and a connection node of the first resistor and the second resistor is connected with the third diode.

5. The novel automatic zero-stabilizing direct-current coupling receiver according to claim 4, characterized in that: the first diode and the second diode are SDP diodes, and the third diode is a common diode.