CN-121984493-A - RS485 driver control circuit

CN121984493ACN 121984493 ACN121984493 ACN 121984493ACN-121984493-A

Abstract

The invention relates to an RS485 driver control circuit, which relates to the integrated circuit technology and comprises a three-state inverter, a switching tube push-pull output circuit and a bias circuit, wherein the switching tube push-pull output circuit comprises a first high-voltage DEMOS tube, a current output end of the first high-voltage DEMOS tube is connected with a reference point Vpx, a first switching tube is arranged between a gate end and the reference point Vpx, the gate end of the second high-voltage DEMOS tube is connected with the reference point Vpx, the current output end of the second high-voltage DEMOS tube is connected with a bus connection end, a second switching tube is arranged between the gate end and the reference point Vpx, the gate end of the third high-voltage DEMOS tube is connected with the bus connection end, the current output end of the third high-voltage DEMOS tube is connected with a negative push-pull input end, the fourth high-voltage DEMOS tube is connected with the reference point Vnx, the current output end of the fourth high-voltage DEMOS tube is grounded, a fourth switching tube is arranged between the gate end and the reference point Vnx, and the gate end of the fourth high-voltage DEMOS tube is connected with the negative push-pull control end. The invention improves the data transmission rate and push-pull output swing.

Inventors

MA YUCHAO
XIONG QIANKUN
LI SIJIA
JIAN HAO
ZHANG CUIXIAN
WANG HONGJUN
ZENG HUA
WANG HUA

Assignees

成都环宇芯科技有限公司

Dates

Publication Date: 20260505
Application Date: 20251230

Claims (5)

The RS485 driver control circuit is characterized by comprising a tri-state inverter, a switching tube push-pull output circuit and a biasing circuit, wherein the switching tube push-pull output circuit comprises: the first high-voltage DEMOS tube is characterized in that a current input end of the first high-voltage DEMOS tube is connected with a power supply VCC, a current output end of the first high-voltage DEMOS tube is connected with a reference point Vpx, a first switch tube is arranged between a gate end and the reference point Vpx, and the gate end is connected with a positive push-pull control end Vctrlp; the current input end of the second high-voltage DEMOS tube is connected with the reference point Vpx, the current output end of the second high-voltage DEMOS tube is connected with the bus connecting end, a second switching tube is arranged between the gate end and the reference point Vpx, and the gate end is connected with the positive push-pull input end Vinp; The current input end of the third high-voltage DEMOS tube is connected with the bus connecting end, the current output end of the third high-voltage DEMOS tube is connected with the reference point Vnx, a third switching tube is arranged between the gate end and the reference point Vnx, and the gate end is connected with the negative push-pull input end Vinn; A fourth high voltage DEMOS tube, the current input end of which is connected with the reference point Vnx, the current output end of which is connected with the ground VSS, a fourth switching tube is arranged between the gate end and the reference point Vnx, and the gate end is connected with the negative push-pull control end Vctrln.
2. The RS485 driver control circuit according to claim 1, wherein the first and second high voltage DEMOS tubes are P-type MOS tubes, and the third and fourth high voltage DEMOS tubes are N-type MOS tubes.
3. The RS485 driver control circuit according to claim 2, The first switch tube is a P-type MOS tube, the drain electrode of the first switch tube is connected with the grid electrode of the first high-voltage DEMOS tube, the source electrode of the first switch tube is connected with the reference point Vpx, and the grid electrode of the first switch tube is connected with the positive output end Vtp of the bias circuit; the second switch tube is a P-type MOS tube, the drain electrode of the second switch tube is connected with the grid electrode of the second high-voltage DEMOS tube, the source electrode of the second switch tube is connected with the reference point Vpx, and the grid electrode of the second switch tube is connected with the positive output end Vtp of the bias circuit; The third switching tube is an N-type MOS tube, the drain electrode of the third switching tube is connected with the grid electrode of the third high-voltage DEMOS tube, the source electrode of the third switching tube is connected with the reference point Vnx, and the grid electrode of the third switching tube is connected with the negative output end Vtn of the biasing circuit; the fourth switching tube is an N-type MOS tube, the drain electrode of the fourth switching tube is connected with the grid electrode of the fourth high-voltage DEMOS tube, the source electrode of the fourth switching tube is connected with the reference point Vnx, and the grid electrode of the fourth switching tube is connected with the negative output end Vtn of the biasing circuit.
4. The RS485 driver control circuit according to claim 3, wherein said tri-state inverter comprises: the source end of the PMOS tube MP12 is connected with the power supply VCC, and the gate end of the PMOS tube MP is connected with the positive enabling end ENP; the drain end of the PMOS tube MP13 is connected with the drain end of the PMOS tube MP12, and the gate end and the source end of the PMOS tube MP13 are connected with the positive push-pull control end Vctrlp; The drain end of the NMOS tube MN12 is connected with the positive push-pull control end Vctrlp, the gate end of the NMOS tube MN is connected with the positive enabling end ENP, and the source end of the NMOS tube MN is grounded; The source end of the PMOS tube MP14 is connected with the power supply VCC, and the gate end of the PMOS tube MP is connected with the tri-state positive control end DINP; the drain end of the PMOS tube MP15 is connected with the drain end of the PMOS tube MP14, the gate end of the PMOS tube MP15 is connected with the positive push-pull control end Vctrlp, and the source end of the PMOS tube MP is connected with the positive push-pull input end Vinp; The drain of NMOS tube MN13 is connected with the drain of PMOS tube MP15, its gate end connects with tri-state the positive control terminal DINP is used for controlling the operation of the memory cell, the source end is grounded; The PMOS tube MP16, the source of which is connected with the power supply VCC, the gate of which is connected with the negative enabling end ENN, and the drain of which is connected with the negative push-pull control end Vctrln; The drain end of the PMOS tube MP17 is connected with the drain end of the PMOS tube MP16, and the gate end of the PMOS tube MP17 is connected with the source end; the drain end of the NMOS tube MN14 is connected with the source end of the PMOS tube MP17, the gate end of the NMOS tube MN is connected with the negative enabling end ENN, and the source end is grounded; The PMOS tube MP18, the source of which is connected with the power VCC, the gate of which is connected with the tri-state negative control end DINN, and the drain of which is connected with the negative push-pull input end Vinn; The source end of the PMOS tube MP19 is connected with the drain end of the PMOS tube MP18, and the gate end of the PMOS tube MP19 is connected with the negative push-pull control end Vctrln; the drain end of the NMOS tube MN15 is connected with the drain end of the PMOS tube MP19, the gate end of the NMOS tube MN is connected with the tri-state negative control end DINN, and the source end of the NMOS tube MN is grounded.
5. The RS485 driver control circuit of claim 3, wherein the switching tube biasing circuit comprises a positive leg and a negative leg, The negative branch includes: the grid electrodes of the PMOS tube MP10 and the PMOS tube MP11 are connected, the source electrode of the PMOS tube MP10 is connected with the power supply VCC, the grid electrode and the drain electrode of the PMOS tube MP10 are connected with the current source, and the drain electrode of the PMOS tube MP11 is connected with the negative output end Vtn of the bias circuit; the source of the PMOS tube MP30 is connected with the power VCC, the drain electrode is connected with the grid electrode of the PMOS tube MP11, and the grid electrode is connected with the negative bias control end ENN; NMOS tube MN7, its grid and drain electrode connect bias circuit negative output terminal Vtn; the grid electrode and the drain electrode of the NMOS tube MN6 are connected with the source electrode of the NMOS tube MN 7; The source electrode of the NMOS tube MN5 is connected with the source electrode of the NMOS tube MN6, the grid electrode of the NMOS tube MN5 is connected with the negative output end Vtn of the bias circuit, and the drain electrode of the NMOS tube MN5 is connected with the RS485 differential bus; NMOS tube MN8, its grid and source connect bias circuit negative output terminal Vtn; the drain electrode of the NMOS tube MN9 is connected with the drain electrode of the NMOS tube MN8, the source electrode of the NMOS tube MN8 is grounded, and the negative bias control end ENN is connected with the grid electrode of the NMOS tube MN9 through an inverter; The positive branch includes: NMOS tube MN10 and NMOS tube MN11, the grid electrode of the NMOS tube MN10 and the grid electrode of the NMOS tube MN11 are connected, the source electrode of the NMOS tube MN10 is connected with the ground VSS, the grid electrode and the drain electrode of the NMOS tube MN10 are connected with a current source, and the drain electrode of the NMOS tube MN11 is connected with a positive output end Vtp of a bias circuit; the source electrode of the NMOS tube MN30 is grounded to VSS, the drain electrode of the NMOS tube MN11 is connected to the grid electrode of the NMOS tube MN11, and the grid electrode of the NMOS tube MN30 is connected to the positive bias control end ENP; the grid electrode and the drain electrode of the PMOS tube MP7 are connected with the positive output end Vtp of the bias circuit; the grid electrode and the drain electrode of the PMOS tube MP6 are connected with the source electrode of the PMOS tube MP 7; the source electrode of the PMOS tube MP5 is connected with the source electrode of the PMOS tube MP6, the grid electrode of the PMOS tube is connected with the positive output end Vtp of the bias circuit, and the drain electrode of the PMOS tube is connected with the RS485 differential bus; the grid and the source of the PMOS tube MP8 are connected with the positive output end Vtp of the bias circuit; The drain of the PMOS tube MP9 is connected with the drain of the PMOS tube MP8, the source power supply VCC, The positive bias control end ENP is connected with the grid electrode of the PMOS tube MP9 through an inverter.

Description

RS485 driver control circuit Technical Field The present invention relates to integrated circuit technology. Background The RS485 transceiver is derived from the industry communication development needs. In industries such as industrial automation, power communication, and intelligent instruments, reliable long-distance communication is required between devices. The early RS-232 communication interface has the defects of short transmission distance, weak anti-interference capability and the like, and cannot meet the communication requirement under the complex industrial environment. In this context, RS485 has been developed that uses a combination of balanced drivers and differential receivers to greatly enhance the ability to resist common mode interference and to enable stable data transmission in complex electromagnetic environments. The data transmission rate is high and can reach 10Mbps at the highest, the transmission distance is long, the transmission rate can reach 100Kbps when the transmission distance is 1200m, the multi-node connection is supported, 32 nodes can be supported generally, and devices with different positions and different functions can be connected into a network to realize data interaction and cooperative work. The RS485 adopts a differential transmission mode, and the driver circuit also inherits the advantage. The differential signal can effectively resist electromagnetic interference and lightning interference, can reduce the influence of external interference on communication data in an industrial environment, ensures the effectiveness of data transmission, and can better communicate in factory workshops where a large number of electromagnetic interference sources such as motors, frequency converters and the like exist. Although RS485 has many advantages, there are some inherent drawbacks in practical applications, particularly in terms of driver design and system stability: The communication speed is limited by a hardware switching mechanism, the automatic receiving and transmitting switching circuit possibly generates state switching delay when the baud rate is high, so that a receiving end misjudges signals to cause communication abnormality, the driving capability is weak, the long-distance communication risk is high, signal attenuation is easy to generate under the condition of long cables or multiple loads to influence the communication quality, the conflict is easy to be caused by lacking a bus arbitration mechanism, multiple master competition and automatic arbitration cannot be realized by adopting a master polling mode like a CAN bus, the bus utilization rate is low, the instantaneity is poor, the whole network is possibly paralyzed due to single-point faults, if a driver of a certain node is damaged and continuously occupies the bus (such as repeatedly transmitting invalid data), the whole network is possibly paralyzed, the fault positioning is difficult, the external interference is sensitive, the extra protection circuit is needed, static electricity, lightning stroke or common mode voltage is in an exceeding range (-7V to +12V), the junction capacitance introduced by the peripheral protection circuit CAN influence the waveform integrity, the reflection and the interference are easy to be caused by the wiring irregularity, the reflection and the topology are not used, the signal reflection is easy to be caused, and the communication stability is reduced. As described above, the RS485 transceiver has the advantages of strong anti-interference capability, long transmission distance, support for multipoint communication, and the like, and is an essential basic interface technology in the industrial communication field. However, it has a significantly short board in terms of high-speed communication stability, driving capability, network fault tolerance, and wiring normalization. In response to these problems, the industry has developed a range of sophisticated optimization schemes including the use of high performance isolated transceivers, the rational configuration of terminals and bias resistors, the use of repeater extension networks, enhanced EMC protection designs, and the like. In the future, along with the improvement of integration level and the embedding of intelligent functions (such as automatic baud rate identification and fault diagnosis), the RS485 can further expand the application scene in the edge computing and hybrid networking while maintaining the cost advantage. Disclosure of Invention Aiming at the problems of low maximum transmission rate, reduced output swing of a driver and large common-mode voltage difference caused by uneven ground potential of long-distance communication under the condition of low power supply voltage, the invention provides a control circuit for switching working modes according to bus terminal voltage, which is designed by using a thin gate oxide device and a push-pull output stage by using a MOS device. The technical sc