Signal transmission circuit and snubber circuit

Abstract

To suppress a current flowing in an unnecessary path in a transformer that does not have a center tap.SOLUTION: A signal transmission circuit is used for transmitting a signal from a first system on a transmitting side to a second system on a receiving side. The first system includes an inductor, a first current source, controlled by a first switch, a second current source, connected in series with the first current source via the inductor and controlled by a second switch, a third switch, connected in parallel with the first current source for controlling a connection with a ground point, and a fourth switch, connected in parallel with the second current source for controlling a connection with the ground point.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to a signal transmission circuit and a snubber circuit.

Background Art

[0002] In digital isolators and the like, non-contact signal transmission and reception via an inductor are performed. These circuits suppress the flow of excessive current into the circuit by providing a center tap between the inductors. On the other hand, for example, due to reasons such as miniaturization of the device, the center tap may not be arranged. In such a case where the center tap is not arranged, a problem may occur in that current flows through the snubber circuit on the transmission side.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Therefore, one of the non-limiting problems to be solved by the embodiments is to suppress the current flowing through an unnecessary path in a transformer without a center tap.

Means for Solving the Problems

[0005] According to one embodiment, a signal transmission circuit is a circuit that transmits a signal from a first system on the transmission side to a second system on the reception side. The first system includes an inductor, a first current source controlled by a first switch, a second current source connected in series via the first current source and the inductor and controlled by a second switch, a third switch connected in parallel with the first current source and controlling the connection to a ground point, and a fourth switch connected in parallel with the second current source and controlling the connection to the ground point. [Brief explanation of the drawing]

[0006] [Figure 1] A schematic diagram showing an example of a digital isolator according to one embodiment. [Figure 2] A schematic diagram showing an example of a transformer section according to one embodiment. [Figure 3] A schematic diagram showing an example of a transformer section according to one embodiment. [Figure 4] A schematic diagram showing an example of a transformer section according to one embodiment. [Figure 5] A schematic diagram showing an example of a transformer section according to one embodiment. [Modes for carrying out the invention]

[0007] The embodiments will be described below with reference to the drawings.

[0008] Figure 1 shows an example of a digital isolator according to one embodiment. The embodiments described herein can be applied to such general digital isolators.

[0009] Digital isolator 1 is a circuit that uses conductors to rectify the differential signals (input differential signals INP / INN) input from the primary side (first system side) through an isolated region and output them to the secondary side (second system side) (output differential signals OUTP / OUTN). Digital isolator 1 transmits the rectified signal via transformer section 10.

[0010] The differential signal input to the first system (transmitter side, primary side) is ΔΣ modulated in the ΔΣ modulator 20, and if necessary, data modulated in the data modulator 24 via the buffer 22, and input to the snubber circuit 28 via the driver 26.

[0011] The snubber circuit 28 is provided in the transformer section 10. In the first system, a noise-controlled signal is propagated to the conductor via this snubber circuit 28, and the signal propagated to the second system by conductance is output after high-frequency noise is suppressed via the snubber circuit 48 in the second system.

[0012] The signal output in the first channel is amplified by amplifier 30, decoded by clock decoder 32, and fed back to ΔΣ modulator 20 via buffer 34 as needed.

[0013] On the second system side (receiving side, secondary side), the signal received in the transformer section 10 via the snubber circuit 48 is amplified in the amplifier 50, the data is decoded in the data decoder 52, the digital signal is converted to an analog signal in the DAC 56, and the signal is output through filters such as the low-pass filter 58 as needed.

[0014] On the second system side, a signal generator 40 generates a clock signal, a clock modulator 44 modulates the clock signal based on this clock signal and controls the snubber circuit 48 via the driver 46, and also uses this clock signal to perform digital-to-analog signal conversion in the DAC 56, thereby appropriately converting the signal received by the conductor into an analog signal and outputting it.

[0015] This disclosure describes a snubber circuit that does not have a center tap to prevent current that may be generated in the transformer section 10 from flowing to an undesirable path.

[0016] (First Embodiment) The transformer section 10 includes a snubber circuit, a primary conductor that performs signal transmission and reception in an isolated state, and a secondary conductor.

[0017] FIG. 2 is a circuit diagram schematically showing an example of a transformer section according to an embodiment. The transformer section 10 includes conductors 100 and 102, switches Sw1, Sw2, Sw3, and Sw4, current sources I1 and I2, resistors R1, R2, R5, and R6, capacitors C1 and C2, and a filter 104.

[0018] The current source I1 is connected to one end of the conductor 100 and is connected to the ground point via the switch Sw1. By turning on / off the switch Sw1, a signal is transmitted to the conductor 100 by the current output from the current source I1.

[0019] The switch Sw1 is connected between the current source I1 and the ground point. The signal transmitted from the first system to the second system is converted by the driver 26 in FIG. 1 to turn on / off the switch Sw1.

[0020] The current source I2 is connected to the other end of the conductor 100 and is connected to the ground point via the switch Sw2. By turning on / off the switch Sw2, a signal is transmitted to the conductor 100 by the current output from the current source I2.

[0021] The switch Sw2 is connected between the current source I2 and the ground point. The signal transmitted from the first system to the second system is converted by the driver 26 in FIG. 1 to turn on / off the switch Sw2.

[0022] The driver 26 generates drive voltages for the respective switches so that the switch Sw1 conducts appropriately for the positive-direction signal of the differential signal and the switch Sw2 conducts appropriately for the negative-direction signal, and drives the respective switches.

[0023] Signals transmitted and received through isolation are converted into pulse signals by, for example, the data modulator 24 in Figure 1. This conversion allows for the transmission of signals in the positive and negative directions, respectively, by switching switches Sw1 and Sw2 on and off.

[0024] In other words, differential signals are generated by current sources I1 and I2, and switches Sw1 and Sw2, and transmitted to the second system via conductors 100 and 102.

[0025] Switches Sw1 and Sw2 are controlled, for example, so that they do not turn on at the same time.

[0026] Resistor R1 and capacitor C1 are connected in series between one end of inductor 100 and ground. Resistor R1 and capacitor C1 form a first filter circuit 120 that acts as part of a filter for the signal oscillating in the current source I1 and switch Sw1. The first filter circuit 120 is connected in parallel with the current source I1 and switch Sw1, as shown in the figure. As an example, this resistor R1 and capacitor C1 act as part of a low-pass filter.

[0027] The resistor R2 and capacitor C2 are connected in series between the other end of the inductor 100 and the ground point. The resistor R2 and capacitor C2 form a second filter circuit 122 that acts as part of the filter for the signal oscillating in the current source I2 and switch Sw2. The second filter circuit 122 is connected in parallel with the current source I2 and switch Sw2, as shown in the figure. As an example, this resistor R2 and capacitor C2 act as part of a low-pass filter.

[0028] Switch Sw3 is connected between one end of inductor 100 and the ground point. Switch Sw3 is a switch that operates in sync with switch Sw2. Switch Sw3 is oscillated by the current source I2 and switch Sw2, and directs current to the ground point so that the signal transmitted through inductor 100 does not affect other elements of the circuit.

[0029] Switch Sw4 is connected between the other end of inductor 100 and the ground point. Switch Sw4 is a switch that is driven in sync with switch Sw1. Switch Sw4 is oscillated by the current source I1 and switch Sw1, and directs current to the ground point so that the signal transmitted through inductor 100 does not affect other elements of the circuit.

[0030] Current flows through inductor 100 in the direction defined by switches Sw1 and Sw2 as described above.

[0031] Inductor 102 is positioned to mutually induce with inductor 100 and is an element that conducts current based on the magnetic field generated by the change in current flowing through inductor 100.

[0032] Resistor R5 is connected between one end of inductor 102 and the ground point.

[0033] Resistor R6 is connected between the other end of inductor 102 and the ground point.

[0034] Filter 104 filters and propagates the potential difference across the inductor 102, which is based on the current generated in the inductor. For example, filter 104 suppresses harmonic components (noise components) and outputs a signal.

[0035] Figure 3 shows the on / off states of the switches of the transformer section 10 according to one embodiment. As described above, switches Sw1 and Sw4 operate synchronously, and switches Sw2 and Sw3 operate synchronously. Figure 3 shows the state where switches Sw1 and Sw4 are on and switches Sw2 and Sw3 are off.

[0036] At this time, switch Sw1 is turned on, and the current generated by current source I1 is filtered through the first filter circuit 120, and current i TX This current i flows to inductor 100. TX The time change of current due to the generation of is the voltage v in inductor 100. TX This generates a pulse signal, and through inductors 100, 102 and filter 104, this pulse signal is filtered through a low-pass filter (voltage v FIL It will be output as ).

[0037] The current that passes through inductor 100 flows to ground via the ON switch Sw4. As a result, excess current is prevented from flowing to other components of the circuit.

[0038] The same operation can be used to suppress excess current when switches Sw2 and Sw3 are turned on synchronously.

[0039] As described above, according to this embodiment, by forming a path in the snubber circuit through which current flows to the ground point, it is possible to suppress the flow of excess current to unintended circuit elements. By using this snubber circuit, harmonic noise can be removed while avoiding the placement of a center tap on the inductor. As a result, it is possible to reduce the circuit area and improve the flexibility of the circuit layout while maintaining characteristics equivalent to those with a center tap.

[0040] Figure 4 is a circuit diagram showing an example of the implementation of the transformer section 10. As shown in Figure 4, each switch may be a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). Each switch can be formed in particular from an n-type MOSFET.

[0041] (Second Embodiment) Figure 5 shows an example of the transformer section 10 according to the second embodiment. The transformer section 10 forms a third filter circuit 124 and a fourth filter circuit 126 instead of the first filter circuit 120 and the second filter circuit 122 in the above-described embodiment.

[0042] The third filter circuit 124 is formed by a resistor R3 and a capacitor C3 connected in series between one end of the inductor 100 and a ground point. The resistor R3 is connected to the ground point via a switch Sw3. The capacitor C3 is connected in parallel with the switch Sw3 from the node where it connects to the resistor R3.

[0043] The fourth filter circuit 126 is formed by a resistor R4 and a capacitor C4 connected in series between the other end of the inductor 100 and the ground point. The resistor R4 is connected to the ground point via a switch Sw4. The capacitor C4 is connected in parallel with the switch Sw4 from the node where it connects to the resistor R4.

[0044] When switches Sw1 and Sw4 are turned on, resistor R3 and capacitor C3 operate as part of the filter, as in the previously described embodiment. Meanwhile, the current propagated through inductor 100 flows to ground through resistor R4 and switch Sw4.

[0045] The arrangement of the filter circuit and switches can also be changed in this way.

[0046] In the two embodiments described above, the filter circuit is provided on the first system side, but the system is not limited to this. Even if there are other circuit elements arranged in the snubber circuit, the excess high-frequency current flowing to those elements can be suppressed by switching the switch in the same way.

[0047] In other words, the digital isolator in this disclosure is a circuit that transmits a signal from a first system to a second system and includes a snubber circuit. The snubber circuit may be configured to include a first current source, a first switch that controls the current flowing from the first current source, a second current source, a second switch that controls the current flowing from the second current source, a third switch connected in parallel with the first current source and controlling the connection to a ground point, and a fourth switch connected in parallel with the second current source and controlling the connection to a ground point. The first and fourth switches turn on / off synchronously, and the second and third switches turn on / off synchronously. The first and second switches turn on exclusively.

[0048] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of Symbols]

[0049] 1: Digital isolator, 10: Transformer section, 100, 102: Conductor, 104: Filter, 120: First filter circuit, 122: Second filter circuit, 124: Third filter circuit, 126: Fourth filter circuit, C1, C2, C3, C4: Capacitors, I1, I2: current source, R1, R2, R3, R4, R5, R6: resistance, Sw1, Sw2, Sw3, Sw4: Switches

Claims

1. A circuit that transmits a signal from the first system on the transmitting side to the second system on the receiving side, The first system is, Inductor and A first current source controlled by a first switch, A second current source is connected in series with the first current source via the inductor and controlled by a second switch, A third switch is connected in parallel with the first current source and controls the connection to the ground point, A fourth switch, connected in parallel with the second current source, controls the connection to the ground point, Equipped with, Signal transmission circuit.

2. The first switch and the third switch are synchronized in their on and off states. The second and fourth switches are synchronized in their on and off states. The first switch and the second switch do not turn on at the same time. The signal transmission circuit according to claim 1.

3. The aforementioned first system further, A first filter circuit is connected in parallel with the third switch to the ground point, A second filter circuit is connected in parallel with the fourth switch to the ground point, Equipped with, A signal transmission circuit according to claim 1 or claim 2.

4. The first filter circuit comprises a first resistor and a first capacitor connected in series, The second filter circuit comprises a second resistor and a second capacitor connected in series. The signal transmission circuit according to claim 3.

5. The aforementioned first system further, A third filter circuit is connected to the third switch, with a portion of it connected in series and a portion of it connected in parallel to the ground point. A fourth filter circuit is provided, with a portion connected in series with the fourth switch and a portion connected in parallel with the ground point. Equipped with, A signal transmission circuit according to claim 1 or claim 2.

6. The third filter circuit is, A third resistor is connected in series with the third switch, A third capacitor is connected in parallel with the third switch and in series with the third resistor, Equipped with, The fourth filter circuit is, A fourth resistor is connected in series with the fourth switch, A fourth capacitor is connected in parallel with the fourth switch and in series with the fourth resistor, It is equipped with. The signal transmission circuit according to claim 5.

7. A circuit that controls the current flowing through an inductor, A first current source controlled by a first switch, A second current source is connected in series with the first current source via the inductor and controlled by a second switch, A third switch is connected in parallel with the first current source and controls the connection to the ground point, A fourth switch, connected in parallel with the second current source, controls the connection to the ground point, Equipped with, Snubber circuit.

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