A two-wire protocol sending circuit and a two-wire transmitter

Abstract

The present invention relates to the field of electrical signal transmission, and discloses a two-wire protocol sending circuit and a two-wire transmitter. The circuit includes: a first amplifier, a resistor, a first transistor, and a second transistor; the positive input terminal of the first amplifier is connected to the first end of the resistor, the second end of the resistor is grounded, the output terminal of the first amplifier is respectively connected to the first ends of the first transistor and the second transistor, the second end of the first transistor is connected to the first end of the resistor, the third end and the second end of the second transistor are respectively connected to a receiving unit through the positive terminal and the negative terminal of an external loop, and the third end of the first transistor, the third end of the second transistor, and the power supply terminal of the first amplifier are all connected to the power supply voltage terminal of the circuit; by adjusting the ratio of the number of the second transistor to the first transistor, a control current signal of 4-20 mA is controlled to be output by the circuit, and compared with the control method and circuit structure of a traditional typical circuit, it is simpler, reduces the chip area, and is beneficial to reducing the chip manufacturing process cost.

Description

Technical Field

[0001] The present invention relates to the field of electrical signal transmission, and particularly to a two-wire protocol sending circuit and a two-wire transmitter. Background Art

[0002] Two-wire system combines the power supply line and the signal line into one, and communication and power supply are achieved through two wires. The two-wire system saves construction and cable costs, bringing great convenience to on-site construction and later maintenance. The most widely used standard analog electrical signal in industry is to transmit analog quantities with 4 - 20 mA DC current, which is not easily interfered, and the internal resistance of the current source is infinite. The wire resistance in series in the loop does not affect the accuracy, and it can be transmitted for hundreds of meters on ordinary twisted pairs. Therefore, the two-wire protocol is widely used in industrial control, such as Figure 1 shown.

[0003] In the prior art, as Figure 2 shows the structure of a typical two-wire protocol sending circuit, which is composed of a bipolar transistor, a voltage regulator, an amplifier, and two resistors; however, due to the complex structure of this typical circuit, the chip area is large, resulting in high chip manufacturing process costs. Summary of the Invention

[0004] The present invention aims to simplify the structure of the two-wire protocol sending circuit, so as to make the chip area smaller and reduce the chip manufacturing process costs; it solves the technical problem of the complex structure of the two-wire protocol sending circuit in the prior art.

[0005] The above invention object is mainly achieved through the following technical solutions:

[0006] In a first aspect, a two-wire protocol sending circuit is applied to a two-wire transmitter. The transmitter includes a sending unit and a receiving unit. The sending unit is used to convert the measured physical quantity into an electrical signal, and then perform signal processing on the electrical signal to generate a voltage control signal. The two-wire protocol sending circuit is used to output a 4 - 20 mA current control signal according to the voltage control signal. The receiving unit is used to convert the current control signal into a corresponding voltage signal and output it, thereby completing the transmission of the electrical signal; the two-wire protocol sending circuit includes:

[0007] A first amplifier, a resistor, a first transistor, and a second transistor;

[0008] The output terminal of the sending unit is connected to the negative input terminal of the first amplifier. The positive input terminal of the first amplifier is connected to the first end of the resistor. The second end of the resistor is grounded. The output terminal of the first amplifier is respectively connected to the first ends of the first transistor and the second transistor. The second end of the first transistor is connected to the first end of the resistor. The third end and the second end of the second transistor are respectively connected to the receiving unit through the positive and negative terminals of the external loop. The third end of the first transistor, the third end of the second transistor and the power supply terminal of the first amplifier are all connected to the power supply voltage terminal of the circuit.

[0009] In a second aspect, a two-wire transmitter includes:

[0010] A sending unit, configured to convert a measured physical quantity into an electrical signal, and perform signal processing on the electrical signal to generate a voltage control signal;

[0011] A two-wire protocol sending circuit according to any one of claims 1 to 5, configured to output a 4-20 mA current control signal according to the voltage control signal;

[0012] A receiving unit, configured to convert the current control signal into a corresponding voltage signal and output it, thereby completing the transmission of the electrical signal.

[0013] Advantages compared with the prior art: A two-wire protocol sending circuit disclosed in the present invention uses fewer resistors compared with a traditional typical two-wire protocol sending circuit. It does not require the use of a sigma-delta DAC control and directly uses a voltage signal for control. The control method is simpler, and the circuit structure is also simpler, making the chip area smaller, which is beneficial to reducing the chip manufacturing process cost; it solves the technical problem of the complex structure of the two-wire protocol sending circuit in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Shows a schematic diagram of the application of the two-wire protocol in the prior art;

[0015] Figure 2 Shows a schematic structural diagram of a typical two-wire protocol sending circuit in the prior art;

[0016] Figure 3 Shows a schematic structural diagram of a two-wire protocol sending circuit in the present application;

[0017] Figure 4 Shows a schematic parallel structure diagram of a two-wire protocol sending circuit in the present application;

[0018] Figure 5 Shows a schematic structural diagram of another two-wire protocol sending circuit in the present application;

[0019] Figure 6 Shows a schematic diagram of the parallel structure of another two-wire protocol transmission circuit in the present application;

[0020] Figure 7 Shows a schematic diagram of the structure of the receiving unit of a two-wire transmitter in the present application. Detailed implementation manners

[0021] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0022] An embodiment of the present application provides a two-wire protocol transmission circuit, which is applied to a two-wire transmitter. The transmitter includes a sending unit and a receiving unit. The sending unit is used to convert the measured physical quantity into an electrical signal, and then perform signal processing on the electrical signal to generate a voltage control signal VCTR. The two-wire protocol transmission circuit is used to output a 4-20 mA current control signal according to the voltage control signal VCTR. The receiving unit is used to convert the current control signal into a corresponding voltage signal and output it, so as to complete the transmission of the electrical signal.

[0023] As Figure 3 shown, the two-wire protocol transmission circuit includes: a first amplifier A1, a resistor R1, a first field-effect transistor M1, and a second field-effect transistor M2. The output end of the sending unit is connected to the negative input end of the first amplifier A1. The positive input end of the first amplifier A1 is connected to the first end of the resistor R1. The second end of the resistor R1 is grounded. The output end of the first amplifier A1 is respectively connected to the gate terminals G1 and G2 of the first field-effect transistor M1 and the second field-effect transistor M2. The drain terminal D1 of the first field-effect transistor M1 is connected to the first end of the resistor R1. The source terminal S2 and the drain terminal D2 of the second field-effect transistor M2 are respectively connected to the receiving unit through the positive terminal Loop + and the negative terminal Loop - of the external loop. The source terminal S1 of the first field-effect transistor M1, the source terminal S2 of the second field-effect transistor, and the power supply terminal of the first amplifier A1 are all connected to the power supply voltage terminal VCC of the circuit.

[0024] In a preferred embodiment, the ratio of the number of the second field effect transistors M2 to the number of the first field effect transistors M1 is N, where N is a positive integer, that is, the number of the second field effect transistors M2 is N times that of the first field effect transistors M1.

[0025] It should be noted that the specific principle of the circuit is as follows:

[0026] The control voltage signal VCTR is input to the negative input terminal of the first amplifier A1. According to the principle of virtual open and virtual short, the voltage at the in-phase terminal node B of the first amplifier A1 is also VCTR. Then the current I1 flowing through the resistor R1 is:

[0027] Also, since the first amplifier A1 is made of MOS transistors, there is no current at the in-phase terminal and the anti-phase terminal. Therefore, all the current I1 flowing through R1 passes through M1. And because the gate-source voltages of M1 and M2 are equal (the gates and sources of M1 and M2 are respectively connected together), the current I2 flowing through M2 is:

[0028]

[0029] Then the current I1 flowing through M1 is:

[0030]

[0031] where μ P is the mobility of holes. Since M1 and M2 are of the same transistor type, their mobilities are the same. C OX is the capacitance per unit area, and they are of the same size in the same process.

[0032] Also, because the gate-sources of M1 and M2 are connected together, the gate-source voltages V GS1 and V GS2 are of the same magnitude. V TH is the threshold voltage of the MOS transistor. The threshold voltages of MOS transistors of the same type are equal. From formulas (2) and (3), formula (4) is obtained:

[0033]

[0034] In the design of analog integrated circuits, the aspect ratios (i.e., W M / L M , where W M represents the widths of M1 and M2, and L M represents the lengths of M1 and M2) of M1 and M2 are usually the same. As can be seen from the above, the number of M2 is N times that of M1, and formula (4) is improved to (5):

[0035] I2 = I1 * N ··· (5)

[0036] Substitute formula (1) into formula (5) to obtain formula (6):

[0037]

[0038] Therefore, when the ratio of N to resistor R1 is given, a control current signal of 4 - 20 mA can be generated simply by adjusting the control voltage signal VCTR. For example, when the value of N is 10 and the resistor R1 is 1000 Ω, the control voltage signal VCTR only needs to be adjusted in the range of 0.4 - 2 V, and the two-wire protocol transmission circuit can output a control current signal of 4 - 20 mA. Compared with the typical circuit in the prior art, fewer resistors are used, and there is no need to use a sigma - delter DAC control. Instead, a voltage signal control is directly adopted.

[0039] It should be noted that as Figure 4 shown, there may be multiple numbers of the first field - effect transistor M1 and the second field - effect transistor M2, which are connected in parallel. In an analog integrated circuit, multiple parallel - connected MOS transistors are equivalent to one MOS transistor. However, since the magnitude of the current flowing through the first field - effect transistor M1 is limited, usually at the μA level, the current is amplified by adjusting the number of M2, and the number of M2 is N times that of M1. By adjusting the ratio of the number of MOS transistors of the first field - effect transistor M1 and the second field - effect transistor M2, the current ratio can be adjusted, and the current at the μA level can be amplified. Therefore, the setting of I1 can have a smaller current limit, such as 1 - 5 μA, which is beneficial to reducing the internal power consumption of the chip. Therefore, when I1 is given, that is, when the control voltage signal VCTR and the resistor R1 are given, only the value of N, that is, the ratio of the number of the second field - effect transistor M2 to the number of the first field - effect transistor M1, needs to be adjusted to control the two - wire protocol transmission circuit to output a control current signal of 4 - 20 mA. Compared with the control method of the typical circuit in the prior art, the control method is simpler, the circuit structure is also simpler, the chip area is reduced, and it is beneficial to reducing the chip manufacturing process cost.

[0040] Advantages compared with the prior art: A two - wire protocol transmission circuit disclosed in the present invention uses fewer resistors compared with the traditional typical two - wire protocol transmission circuit. There is no need to use a sigma - delter DAC control, and a voltage signal control is directly adopted. The control method is simpler, the circuit structure is also simpler, making the chip area smaller, which is beneficial to reducing the chip manufacturing process cost; it solves the technical problem of the complex structure of the two - wire protocol transmission circuit in the prior art.

[0041] The present invention also provides another two-wire protocol sending circuit, which is applied to a two-wire transmitter. The transmitter includes a sending unit and a receiving unit. The sending unit is used to convert the measured physical quantity into an electrical signal, and then process the electrical signal to generate a voltage control signal VCTR. The two-wire protocol sending circuit is used to output a 4-20 mA current control signal according to the voltage control signal VCTR. The receiving unit is used to convert the current control signal into a corresponding voltage signal and output it, so as to complete the transmission of the electrical signal.

[0042] As Figure 5 shown, the two-wire protocol sending circuit includes: a first amplifier A1, a resistor R1, a first bipolar transistor Q1, and a second bipolar transistor Q2. The output end of the sending unit is connected to the negative input end of the first amplifier A1. The positive input end of the first amplifier A1 is connected to the first end of the resistor R1. The second end of the resistor R1 is grounded. The output end of the first amplifier is respectively connected to the base electrodes b1 and b2 of the first bipolar transistor Q1 and the second bipolar transistor Q2. The collector electrode c1 of the first bipolar transistor is connected to the first end of the resistor. The emitter electrode e2 and the collector electrode c2 of the second bipolar transistor are respectively connected to the receiving unit through the positive end Loop + and the negative end Loop - of the external loop. The emitter electrode e1 of the first bipolar transistor, the emitter electrode e2 of the second bipolar transistor, and the power supply end of the first amplifier A1 are all connected to the power supply voltage end VCC of the circuit.

[0043] In a preferred embodiment, the ratio of the number of the second bipolar transistor Q2 to the number of the first bipolar transistor Q1 is N, and N is a positive integer, that is, the number of the second bipolar transistor Q2 is N times the number of the first bipolar transistor Q1.

[0044] It should be noted that the specific principle of the circuit is as follows:

[0045] The control voltage signal VCTR is input to the negative input end of the first amplifier A1. According to the principle of virtual open and virtual short, the voltage at the in-phase terminal node B of the first amplifier A1 is also VCTR. Then the current I1` flowing through the resistor R1 is:

[0046] Also, since the first amplifier A1 is made of MOS transistors, there is no current at the in-phase terminal and the direction terminal. Therefore, all the current I1` flowing through R1 passes through Q1. And because the base-emitter voltages of Q1 and Q2 are equal (the bases and emitters of Q1 and Q2 are respectively connected together), the current I2` flowing through Q2 is:

[0047]

[0048] Then the current I1` flowing through Q1 is:

[0049]

[0050] where μ P is the mobility of holes. Since Q1 and Q2 are of the same transistor type, their mobilities are the same. C OX is the capacitance per unit area and is the same for the same process.

[0051] Also, since the bases and emitters of Q1 and Q2 are connected together, the base-emitter voltages V be1 and V be2 are of the same magnitude. V TH is the threshold voltage of the MOS transistor. The threshold voltages of MOS transistors of the same type are equal. From equations (8) and (9), equation (10) is obtained:

[0052]

[0053] In the design of analog integrated circuits, the aspect ratios (i.e., W Q / L Q , where W Q represents the widths of Q1 and Q2, and L Q represents the lengths of Q1 and Q2) of Q1 and Q2 are usually the same. As can be seen from the above, the number of Q2 is N times that of Q1, and equation (10) is improved to (11):

[0054] I2` = I1` * N ··· (11)

[0055] Substituting equation (7) into equation (11), equation (12) is obtained:

[0056]

[0057] Therefore, when the ratio of N to the resistor R1 is given, a control current signal of 4 - 20 mA can be generated by simply adjusting the control voltage signal VCTR. For example, when the given N value is 10 and the resistor R1 is 1000 Ω, the control voltage signal VCTR only needs to be adjusted in the range of 0.4 - 2 V, and the two-wire protocol transmission circuit can output a control current signal of 4 - 20 mA. Compared with the typical circuits in the prior art, fewer resistors are used, and there is no need to use a sigma - delter DAC for control. Instead, a voltage signal is directly used for control.

[0058] It should be noted that, as Figure 6As shown, there may be multiple numbers of the first bipolar transistor Q1 and the second bipolar transistor Q2, which are connected in parallel. In an analog integrated circuit, multiple parallel MOS transistors are equivalent to one MOS transistor. However, since the magnitude of the current flowing through the first bipolar transistor Q1 is limited, usually at the uA level. Therefore, the current is amplified by adjusting the number of Q2, and the number of Q2 is N times that of Q1. By adjusting the ratio of the number of MOS transistors of the first bipolar transistor Q1 and the second bipolar transistor Q2, the current ratio can be adjusted, and the current at the uA level can be amplified. Therefore, the setting of I1` can limit the current more minimally, such as 1 to 5 uA, which is beneficial to reducing the internal power consumption of the chip. Therefore, when I1` is given, that is, when the control voltage signal VCTR and the resistor R1 are given, only by adjusting the N value, that is, the ratio of the number of the second bipolar transistor Q2 to the number of the first bipolar transistor Q1, can the control current signal of 4 to 20 mA be output by the two-wire protocol sending circuit. Compared with the control method of the typical circuit in the prior art, the control method is simpler, the circuit structure is also simpler, the chip area is reduced, and it is beneficial to reducing the chip manufacturing process cost.

[0059] Advantages compared with the prior art: A two-wire protocol sending circuit disclosed by the present invention uses fewer resistors compared with the traditional typical two-wire protocol sending circuit. It directly uses a voltage signal for control without using a sigma - delter DAC control. The control method is simpler, the circuit structure is also simpler, making the chip area smaller, which is beneficial to reducing the chip manufacturing process cost; it solves the technical problem of the complex structure of the two-wire protocol sending circuit in the prior art.

[0060] The embodiment of the present invention also provides a two-wire transmitter, including:

[0061] A sending unit, configured to convert the measured physical quantity into an electrical signal, and perform signal processing on the electrical signal to generate a voltage control signal;

[0062] According to any one of the two-wire protocol sending circuits described in the above embodiments, configured to output a current control signal of 4 to 20 mA according to the voltage control signal;

[0063] A receiving unit, configured to convert the current control signal into a corresponding voltage signal and output it, thereby completing the transmission of the electrical signal.

[0064] In a preferred embodiment, as Figure 7 shown, the receiving unit includes:

[0065] A sensing resistor R2 and a second amplifier A2, the positive terminal Loop of the external loop + is connected to the power supply terminal of the second amplifier A2, the negative terminal Loop of the external loop- They are respectively connected to the positive input terminal of the second amplifier A2 and the first end of the sensing resistor R2. The second end of the sensing resistor R2 is respectively connected to the negative input terminal of the second amplifier A2 and the ground terminal; the output terminal of the second amplifier is used to output the voltage signal. The receiving unit converts the 4-20 mA current control signal output by the two-wire protocol sending circuit into a voltage signal through the sensing resistor R2 and amplifies and outputs it with the second amplifier A2.

[0066] The embodiments of the present invention have been introduced in detail above. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A two-wire protocol sending circuit, characterized in that, Applied to a two-wire transmitter, the transmitter includes a sending unit and a receiving unit. The sending unit is used to convert the measured physical quantity into an electrical signal, and then process the electrical signal to generate a voltage control signal. The two-wire protocol sending circuit is used to output a 4-20 mA current control signal according to the voltage control signal. The receiving unit is used to convert the current control signal into a corresponding voltage signal and output it, so as to complete the transmission of the electrical signal; The two-wire protocol sending circuit includes: A first amplifier, a resistor, a first transistor, and a second transistor; The output end of the sending unit is connected to the negative input end of the first amplifier. The positive input end of the first amplifier is connected to the first end of the resistor. The second end of the resistor is grounded. The output end of the first amplifier is respectively connected to the first ends of the first transistor and the second transistor. The second end of the first transistor is connected to the first end of the resistor. The third end and the second end of the second transistor are respectively connected to the receiving unit through the positive and negative ends of the external loop. The third end of the first transistor, the third end of the second transistor, and the power supply end of the first amplifier are all connected to the power supply voltage end of the circuit.

2. The two-wire protocol sending circuit according to claim 1, characterized in that, The ratio of the number of the second transistor to the number of the first transistor is N, and N is a positive integer.

3. The two-wire protocol sending circuit according to claim 1 or 2, characterized in that, The first transistor and the second transistor are field effect transistors or bipolar transistors.

4. The two-wire protocol sending circuit according to claim 3, characterized in that, The first transistor and the second transistor are field effect transistors. The output end of the first amplifier is respectively connected to the gate electrodes of the first field effect transistor and the second field effect transistor. The drain electrode of the first field effect transistor is connected to the first end of the resistor. The source electrode and the drain electrode of the second field effect transistor are respectively connected to the receiving unit through the positive and negative ends of the external loop. The source electrode of the first field effect transistor, the source electrode of the second field effect transistor, and the power supply end of the first amplifier are all connected to the power supply voltage end of the circuit.

5. The two-wire protocol sending circuit according to claim 3, characterized in that, The first transistor and the second transistor are bipolar transistors. The output end of the first amplifier is respectively connected to the base electrodes of the first bipolar transistor and the second bipolar transistor. The collector electrode of the first bipolar transistor is connected to the first end of the resistor. The emitter electrode and the collector electrode of the second bipolar transistor are respectively connected to the receiving unit through the positive and negative ends of the external loop. The emitter electrode of the first bipolar transistor, the emitter electrode of the second bipolar transistor, and the power supply end of the first amplifier are all connected to the power supply voltage end of the circuit.

6. A two-wire transmitter, characterized in that, Includes: A sending unit, which is used to convert the measured physical quantity into an electrical signal and process the electrical signal to generate a voltage control signal; A two-wire protocol sending circuit according to any one of claims 1 to 5, which is used to output a 4-20 mA current control signal according to the voltage control signal; A receiving unit, which is used to convert the current control signal into a corresponding voltage signal and output it, so as to complete the transmission of the electrical signal.

7. The two-wire transmitter according to claim 6, characterized in that, The receiving unit includes: An induction resistor and a second amplifier, the positive terminal of the external loop is connected to the power supply terminal of the second amplifier, the negative terminal of the external loop is respectively connected to the positive input terminal of the second amplifier and the first end of the induction resistor, and the second end of the induction resistor is respectively connected to the negative input terminal of the second amplifier and the ground terminal; the output terminal of the second amplifier is used to output the voltage signal.

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