JP2011223254A - Signal transmitter and current setting method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the reliability of an element from declining.SOLUTION: A signal transmitter comprises a differential pair (3 and 4) which outputs a transmission signal, transmission side load resistors (6 and 7) which can be connected, respectively, between two output ends of the differential pair and a transmission side power supply 10, two variable current sources (13, 14, 15, and 16) connected, respectively, to two output ends of the differential pair and can change the potentials at two output ends of the differential pair in the direction of the ground potential, a comparator 11 which compares the voltages at two output ends of the differential pair, and a controller 12 which sets the current values of two variable current sources. Two output ends of the differential pair are connected to a power supply terminal 23 having a potential higher than that of the transmission side power supply through reception side load resistors 21 and 22, respectively. The controller 12 sets the current values of two variable current sources during signal transmission based on the current value of the variable current source (15 and 16) when the current of the variable current source (15 and 16) is increased in advance of signal transmission so that comparison result of the comparator 11 changes.

Description

  The present invention relates to a signal transmission device and a current setting method thereof, and more particularly to a signal transmission device having a DC coupling interface between a transmitter and a receiver and a current setting method thereof.

  In recent years, in digital AV equipment, a digital video / audio interface has been used instead of an analog video / audio interface. The HDMI standard that appeared in 2002 is a typical example. With the advent of Blu-ray discs and the remarkable progress of video processing technology in thin digital televisions, the transmission speed of digital video / audio interfaces is also increasing. For example, the transmission speed of the HDMI standard has been improved in 2006, and the speed has been increased from 1.65 Gbps to 3.4 Gbps per conventional transmission line set.

  Along with such high-speed interfaces, a signal integrity problem in which transmission signal quality deteriorates due to waveform distortion caused by re-reflection caused by impedance mismatching in the middle of a transmission line such as a connector has become apparent. In view of the above background, in order to absorb a reflected wave to the transmission end caused by impedance mismatch, a transmission termination (Back termination) technology is known that connects a termination resistor that takes impedance matching not only at the reception end but also at the transmission end. It has been. The HDMI standard is defined as a DC-coupled interface, and the prior art discloses a circuit configured to connect a transmission termination resistor between a differential transmission path and a power supply terminal (see Non-Patent Document 1). .

  The prior art will be described with reference to FIG. The transmission device includes a power supply terminal 10, differential input terminals 1 and 2, differential output terminals 17 and 18, a differential pair including NchMOS transistors 3 and 4, a constant current source 5 for the differential pair, Transmission termination resistors 6 and 7 are provided. The output terminals of the differential pair are connected to the differential output terminals 17 and 18, respectively, and are connected to the power supply terminal 10 via the transmission termination resistors 6 and 7, respectively.

  Further, the differential output terminals 17 and 18 are connected to a receiving device having differential input terminals 19 and 20. The receiving device includes a differential receiver 24 having load resistors 21 and 22 connected between a power supply terminal 23 and differential input terminals 19 and 20, respectively, for receiving a differential signal.

Chi-Cheng Ju, et al. "A Multi-Format Blu-ray Player SoC in 90nm CMOS", ISSCC 2009 / SESSION 8 / MULTITIMEDIA PROCESSORS / 8.4, p152-154

  The following analysis is given in the present invention.

In FIG. 3, the power supply voltage of the transmission device applied to the power supply terminal 10 is VDD1, the resistance values of the transmission termination resistors 6 and 7 of the transmission device are RL, the current value of the constant current source 5 is I0, and the reception is applied to the power supply terminal 23. The power supply voltage of the device is VDD2, and the resistance values of the load resistors 21 and 22 of the receiving device are the same RL as the resistance values of the transmission termination resistors 6 and 7. In this case, the high level VH and the low level VL of the single-ended output voltage of each of the differential output terminals 17 and 18 are expressed as follows.
VH = VDD1-0.5 × (VDD1-VDD2)
= 0.5 × (VDD1 + VDD2) (1)
VL = VDD1-0.5 * (VDD1-VDD2) -0.5 * RL * I0
= 0.5 × (VDD1 + VDD2−RL × I0) (2)

  Here, when VDD2> VDD1, VH> VDD1 with respect to VH, and the high-level voltage on the transmission side exceeds the power supply voltage VDD1 of the transmission device. Therefore, there is a possibility that the reliability of the elements in the transmission device is lowered.

  The signal transmission device according to one aspect (side surface) of the present invention is connectable between a differential pair that outputs a transmission signal, and first and second output terminals of the differential pair and a transmission-side power source. Connected to the first and second transmission side load resistors and the first and second output terminals of the differential pair, respectively, and the potentials of the first and second output terminals of the differential pair are respectively set to the ground potential direction. The first and second variable current sources that can be changed to the above, the comparison unit that compares the voltages at the first and second output terminals of the differential pair, and the current values of the first and second variable current sources are set. The first and second output terminals of the differential pair are connected to a receiving-side power source having a higher potential than the transmitting-side power source via first and second receiving-side load resistors, respectively. When the control unit increases the current of the second variable current source prior to signal transmission, the control unit Compare results based on the current value of the second variable current source when changes, to set the first and the current value of the second variable current source at the time of signal transmission.

  The current setting method according to another aspect (side surface) of the present invention is connectable between a differential pair that outputs a transmission signal, and first and second output terminals of the differential pair and a transmission-side power source. Connected to the first and second transmission side load resistors and the first and second output terminals of the differential pair, respectively, and the potentials of the first and second output terminals of the differential pair are respectively set to the ground potential direction. First and second variable current sources that can be changed to each other, and the first and second output terminals of the differential pair are respectively transmitted from the transmission-side power supply via the first and second reception-side load resistors. A method for setting a current of a signal transmission device connected to a high-potential receiving-side power supply, wherein the current of a second variable current source is increased prior to signal transmission. The step of comparing the voltage at the output terminal of the 2 and the second possibility when the comparison result changes. Based on the current value of the current source, comprising the steps of: setting the first and the current value of the second variable current source at the time of signal transmission, the.

  According to the present invention, on the transmission side, the output amplitude does not exceed the power supply voltage, and it is possible to prevent the reliability of elements and the like from being lowered.

1 is a circuit diagram of a signal transmission device according to an embodiment of the present invention. It is a flowchart which shows the control procedure of the control part which concerns on one Example of this invention. It is a circuit diagram of the conventional signal transmission apparatus.

  The signal transmission device according to the embodiment of the present invention includes a differential pair (3 and 4 in FIG. 1) that outputs a transmission signal, first and second output terminals of the differential pair, and a transmission-side power source (in FIG. 1). 1 and the second transmission-side load resistance (corresponding to 6 and 7 in FIG. 1) and the first and second output terminals of the differential pair, respectively. First and second variable current sources (13, 14, 15, 16 in FIG. 1) that are connected and can change the potential of the first and second output terminals of the differential pair in the direction of the ground potential, and differential A comparison unit (11 in FIG. 1) that compares the voltages of the first and second output terminals of the pair; a control unit (12 in FIG. 1) that sets the current values of the first and second variable current sources; The first and second output terminals of the differential pair are respectively connected to the transmission side power supply via the first and second reception side load resistors (21 and 22 in FIG. 1), respectively. When the control unit is connected to a high-potential receiving-side power source (23 in FIG. 1) and the control unit increases the current of the second variable current source prior to signal transmission, the comparison result of the comparison unit changes. Based on the current value of the second variable current source, the current values of the first and second variable current sources during signal transmission are set.

  In the signal transmission device, the driving current value of the differential pair is the same as the maximum current value of the first and second variable current sources, and the first and second transmitting load resistors and the first and second receiving sides The resistance value is the same as that of the load resistance, and the control unit sets the signal levels of the first and second output terminals of the differential pair when setting the current values of the first and second variable current sources during signal transmission. Are set to low level and high level, respectively, the first and second transmission side load resistors are connected and disconnected, respectively, and the currents of the first and second variable current sources are set to 0 respectively. When the current of the second variable current source is increased by controlling to be half of the maximum current value, the voltage at the first output terminal is equal to or higher than the voltage at the second output terminal. Of the second variable current source at the time indicated by the comparison result of the comparison unit The increment signal is set as the first and the current value of the second variable current source at the time of transmission, at the time of signal transmission, the first and second transmission-side load resistor may be connected, respectively.

  In the signal transmission device, each of the first and second variable current sources includes N (N is an integer of 2 or more) current sources, and the control unit individually activates the N current sources. In this case, the current value of the variable current source may be set.

  A semiconductor device may include the signal transmission device described above.

  According to the signal transmission apparatus as described above, the voltage at the first and second output ends does not exceed the voltage of the transmission-side power supply. Therefore, it is possible to prevent the reliability of the elements and the like from being lowered.

  Hereinafter, it will be described in detail with reference to the drawings in accordance with embodiments.

  FIG. 1 is a circuit diagram of a signal transmission apparatus according to an embodiment of the present invention. 1, the same reference numerals as those in FIG. 3 represent the same items, and the description thereof is omitted. The transmission apparatus includes switches 8 and 9 connected between the transmission termination resistors 6 and 7 and the power supply terminal 10, and current source groups 14 and 16 each including N current sources and each having a current value of I0 / N. N switches 13 connected between the individual current sources of the current source group 14 and the differential output terminal 18, and connected between the individual current sources of the current source group 16 and the differential output terminal 17. And a controller 11 for connecting the differential output terminals 17 and 18 to the comparison input, and a control unit 12 for controlling the opening and closing of the switches 13 and 15 using the comparison result of the comparator 11 as an input. Prepare.

  Next, the operation of the signal transmission device will be described. FIG. 2 is a flowchart showing a control procedure of the control unit 12 for setting the opening and closing of the switches 13 and 15 during signal transmission. Here, N is an even number. The control unit 12 executes the following procedure prior to signal transmission.

  In step S1, the differential input terminal 1 is set to a high level and the differential input terminal 2 is set to a low level. NchMOS transistors 3 and 4 are turned on and off, respectively.

  In step S2, the switch 8 is closed (turned on), the switch group 15 is all opened (turned off), the switch 9 is opened (turned off), and the switch group 13 is closed (turned on) by N / 2. A current flowing from the power supply terminal 10 via the transmission terminating resistor 6 and a current flowing from the power supply terminal 23 via the load resistor 21 flow to the constant current source 5 via the NchMOS transistor 3. Further, a current flowing from the power supply terminal 23 through the load resistor 22 flows through the switch group 13 and the current source group 14 that are closed by N / 2. Further, m = 0.

  In step S3, it is determined whether or not the output of the comparator 11 is at a high level. If it is at the high level (Yes in step S3), it indicates that the power supply voltage VDD1 of the transmission device is higher than the power supply voltage VDD2 of the reception device. Therefore, since it is not necessary to operate the current source groups 14 and 16 to lower the potentials of the differential output terminals 17 and 18, the switch 9 is closed and the switch group 13 and the switch group 15 are all opened in step S4.

  On the other hand, when the output of the comparator 11 is at a low level (No in step S3), it indicates that the power supply voltage VDD1 of the transmission device is lower than the power supply voltage VDD2 of the reception device. Therefore, in step S5, the control unit 12 closes the switches of the switch group 13 one by one until the output of the comparator 11 becomes high level (Yes in step S6).

  In step S7, the value of the number m of additionally closed switches when the output of the comparator 11 changes from the low level to the high level is held. Then, the switches 8 and 9 are closed, and only the m switches holding the switch groups 13 and 15 are closed.

  After completing the series of control procedures described above, signals during normal operation are input from the differential input terminals 1 and 2.

  Next, how the voltages of the differential output terminals 17 and 18 become by the above series of control procedures will be described. Here, the power supply voltage of the transmission device to be applied to the power supply terminal 10 is VDD1, the resistance values of the load resistors 6 and 7 of the transmission device are RL, the current value of the constant current source 5 is I0, and The power supply voltage is VDD2, and the resistance values of the load resistors 21 and 22 of the receiving device are the same resistance values RL as the transmission termination resistors 6 and 7.

First, the differential input terminal 1 is set to the high level and the differential input terminal 2 is set to the low level, the switch 8 is closed, the switch group 15 is opened, the switch 9 is opened, and the switch group 13 is closed by N / 2. . The voltages VA and VB of the differential output terminals 17 and 18 at this time are expressed as the following equations (3) and (4).
VA = 0.5 × (VDD1 + VDD2−RL × I0) (3)
VB = VDD2-0.5 × RL × I0 Formula (4)

Therefore, the comparison voltage VA-VB in the comparator 11 is expressed by the equations (3), (4) to (5).
VA−VB = 0.5 × (VDD1−VDD2) (5)

When VA-VB <0, that is, when the output of the comparator 11 is at a low level, the switches of the switch group 13 are sequentially closed, and when the m switches are closed, the output of the comparator 11 changes from a low level to a high level. Suppose. At this time, the voltage VB2 of the differential output terminal 18 is expressed by the following equation (6).
VB2 = VDD2- (0.5 + m / N) × RL × I0 Formula (6)

At this time, since the comparison voltage of the comparator 11 is VA−VB2> 0, the following expression (7) is established.
VA−VB2 = 0.5 × (VDD1−VDD2) + m / N × RL × I0> 0 (7)

The high level VH and the low level VL of each single-ended output voltage at the differential output terminals 17 and 18 when the switches 8 and 9 are closed and the switch groups 13 and 15 are each closed by m switches are as follows: It is expressed as equations (8) and (9).
VH = VDD1- {0.5.times. (VDD1-VDD2) + m / N.times.RL.times.I0} (8)
VL = VDD1- {0.5 * (VDD1-VDD2) + m / N * RL * I0} -0.5 * RL * I0 (9)

  Here, from Expression (7), 0.5 × (VDD1−VDD2) + m / N × RL × I0> 0. Therefore, in Expression (8), VH <VDD1 and the high level voltage VH does not exceed the power supply voltage VDD1. That is, the voltage VH is always lower than the power supply voltage VDD1, and it is possible to prevent the reliability of elements on the transmission side from being lowered.

  It should be noted that the disclosures of the aforementioned patent documents and the like are incorporated herein by reference. Within the scope of the entire disclosure (including claims) of the present invention, the embodiments and examples can be changed and adjusted based on the basic technical concept. Various combinations and selections of various disclosed elements are possible within the scope of the claims of the present invention. That is, the present invention of course includes various variations and modifications that could be made by those skilled in the art according to the entire disclosure including the claims and the technical idea.

1, 2, 19, 20 Differential input terminal 3, 4 Nch MOS transistor 5 Constant current source 6, 7 Transmission termination resistor 8, 9, 13, 15 Switch 10, 23 Power supply terminal 11 Comparator 12 Control unit 14, 16 Current source Groups 17 and 18 Differential output terminals 21 and 22 Load resistance 24 Differential receiver

Claims (5)

A differential pair for outputting a transmission signal;
First and second transmission-side load resistors that are connectable between first and second output terminals of the differential pair and a transmission-side power source, respectively;
First and second variable currents respectively connected to the first and second output terminals of the differential pair and capable of changing the potentials of the first and second output terminals of the differential pair in the direction of the ground potential, respectively. The source,
A comparator for comparing the voltages of the first and second output terminals of the differential pair;
A control unit for setting current values of the first and second variable current sources;
With
The first and second output terminals of the differential pair are connected to a receiving power source having a higher potential than the transmitting power source via first and second receiving load resistors, respectively.
The control unit is based on the current value of the second variable current source when the comparison result of the comparison unit changes when the current of the second variable current source is increased prior to signal transmission. A signal transmission device configured to set current values of the first and second variable current sources during signal transmission. The drive current value of the differential pair is the same as the maximum current value of the first and second variable current sources, and the first and second transmission load resistors and the first and second reception loads The resistance value is the same as the resistance,
When the control unit sets the current values of the first and second variable current sources during signal transmission,
Setting the differential pair so that the signal levels of the first and second output terminals of the differential pair are low level and high level, respectively;
The first and second transmitting load resistors are connected and disconnected,
Controlling the currents of the first and second variable current sources to be 0 and half of the maximum current value, respectively;
When the comparison result of the comparison unit indicates that the voltage of the first output terminal is equal to or higher than the voltage of the second output terminal when the current of the second variable current source is increased. Is set as the current value of the first and second variable current sources at the time of signal transmission,
2. The signal transmission device according to claim 1, wherein the first and second transmission-side load resistors are respectively connected during signal transmission.   Each of the first and second variable current sources includes N (N is an integer of 2 or more) current sources, and the control unit individually activates the N current sources to activate the N current sources. 3. The signal transmission device according to claim 1, wherein a current value of the variable current source is set.   A semiconductor device comprising the signal transmission device according to claim 1. A differential pair for outputting a transmission signal;
First and second transmission-side load resistors that are connectable between first and second output terminals of the differential pair and a transmission-side power source, respectively;
First and second variable currents respectively connected to the first and second output terminals of the differential pair and capable of changing the potentials of the first and second output terminals of the differential pair in the direction of the ground potential, respectively. The source,
And the first and second output terminals of the differential pair are connected to a receiving-side power source having a higher potential than the transmitting-side power source via first and second receiving-side load resistors, respectively. A current setting method,
Comparing the voltages at the first and second output terminals of the differential pair when the current of the second variable current source is increased prior to signal transmission;
Setting the current values of the first and second variable current sources during signal transmission based on the current value of the second variable current source when the comparison result changes;
The current setting method characterized by including.

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