GB2398192A

GB2398192A - Digitally controlled switching signal generator

Info

Publication number: GB2398192A
Application number: GB0302487A
Authority: GB
Inventors: Peter Hartnett
Original assignee: TRANSPARENT ENGINEERING Ltd
Current assignee: TRANSPARENT ENGINEERING Ltd
Priority date: 2003-02-04
Filing date: 2003-02-04
Publication date: 2004-08-11
Anticipated expiration: 2023-02-04
Also published as: GB0302487D0; GB2398192B

Abstract

There is disclosed an electronic device 2 for generating a switching signal output 22, 24, 26 comprising a micro-controller 4, a ramp generator 6, a digital to analogue convertor 8, a plurality of comparators 10, 12, 14, 16 and a logic circuit 18, the micro-controller 4 being arranged to control the ramp generator 6 to generate a ramping signal 7, and to control the digital to analogue convertor 8 to generate a threshold value signal 11, 13, 15, 17 for each of the comparators 10, 12, 14, 16, each of the comparators 10, 12, 14, 16 being arranged to receive for comparing the ramping signal 7 and the threshold value signal 11, 13, 15, 17 so as to produce a comparison signal, and the logic circuit 18 being arranged to receive each of the comparison signals and thereby produce at least one switching signal output 22, 24, 26. There is also disclosed a method of generating a switching signal output.

Description

2398 1 92

IMPROVEMENTS IN OR RELATING TO AN ELECTRONIC DEVICE

The present invention relates to an electronic device, particularly an electronic device for generating a switching signal.

Devices for generating switching or timing signals are used extensively in electronic and electrical devices. A particularly useful type of device is one which produces two complimentary switching signals which can be used, for example, to open and close circuits in a concerted manner.

It is desirable for such devices to generate the switching signals with a high degree of accuracy in the characteristics of the signals, such as the frequency and waveform of each of the switching signals.

Analogue circuitry and components may be used to generate switching signals of high accuracy. However, such analogue devices cannot be readily reprogrammed or altered to change the characteristics, such as the frequency and/or waveform, of the switching signal.

On the other hand, digital circuitry and components can also be used to generate the required high accuracy switching signals, and can be readily reprogrammed to change the frequency and/or waveform thereof. However, such digital devices tend to be relatively expensive and so are not appropriate for every potential use.

The present invention seeks to provide an improved device for generating a switching signal.

According to the present invention there is provided an electronic device for generating a switching signal output comprising a micro-controller, a ramp generator, a digital to analogue convertor, a plurality of comparators and a logic circuit, the micro-controller being arranged to control the ramp generator to generate a ramping signal and to control the digital to analogue convertor to generate a threshold value signal for each of the comparators, each of the comparators being arranged for comparing the ramping signal with the threshold value signal so as to produce a comparison signal, and the logic circuit being arranged to receive each of the comparison signals and thereby produce at least one switching signal output.

Preferably, the device is arranged to produce more than one switching signal.

Conveniently, the device is arranged to produce two switching signals.

Advantageously, the switching signals alternate between a first value and a second value and the transition of one signal between the values is separated by the transition of the other signal between the values in the opposite sense by a deadtime.

Preferably, the device comprises four comparators.

Conveniently, the micro-controller has a memory containing a look-up table for dead time programming.

Advantageously, the device further comprises a communications interface whereby the settings of the micro controller may be altered to modify the characteristics of the at least one switching signal.

Preferably, the characteristics comprise dead times and/or mark space ratios.

Conveniently, the comparators comprise fast comparators.

According to another aspect of the present invention, there is provided a method of generating at least one switching signal comprising the steps of: providing a device comprising a micro-controller, a ramp generator, a digital to analogue convertor, a plurality of comparators and a logic circuit, controlling the ramp generator to generate a ramping signal, controlling the digital to analogue convertor to generate a threshold value signal for each of the comparators, arranging for each of the comparators to compare the ramping signal with the threshold value signal so as to produce a comparison signal, and arranging for the logic circuit to receive the comparison signal from each of the comparators and hereby to produce a switching signal output.

Preferably, the device is arranged to produce more than one switching signal.

Conveniently, the device is arranged to produce two switching signals.

Preferably, the device comprises comparators.

Advantageously, the device further comprises a communications interface and the method further comprises the step of altering the settings of the micro-controller to thereby modify the characteristics of the at least one switching signal.

Preferably, the characteristics comprise dead times and/or mark space ratios.

The present invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a schematic illustration of an electronic device according to the present invention, Figure 2 is an illustration of the switching signals generated by a device of the invention, Figure 3 is an illustration of the relationship between a ramping signal and threshold value signals, and Figure 4 is an illustration of a particular signal waveform.

Turning to figure 1, an electronic device of the present invention is shown schematically at 2. The device 2 is controlled by a microcontroller 4 which controls a ramp generator 6 and a digital to analogue convertor (DAC) 8. The ramp generator 6 generates a ramping signal 7, for example with a saw-tooth waveform. The same ramping signal is supplied to each of four comparators 10, 12, 14 and 16. The DAC 8 provides a threshold value signal 11, 13, 15 and 17 to the four comparators 10, 12, 14 and 16 respectively. Each of the threshold value signals 11, 13, 15 17 provided to each of the four comparators may be the same or different. Each of the four comparators 10, 12, 14 and 16 then compares the ramping signal with its threshold value signal 11, 13, 15, 17 to produce a comparison signal therefrom. The comparison signal output from each of the four comparators 10, 12, 14 and 16 is fed into a logic circuit 18. The logic circuit 18 produces two switching signal outputs based on the signals received from the four comparators 10, 12, 14 and 16. The logic circuit 18 may also comprise means for removing artefacts and other erroneous signals from the circuit.

Suitable logic circuits are referred to as glue logic. Thus, the logic circuit 18 may be arranged to produce a clean switching signal.

There is also provided a communications interface 20 so that the microcontroller 4 can be reprogrammed by connection with an external device, such as a personal computer.

Figure 2 shows the waveforms of the two signal outputs 22 and 24 generated by the device. It can be seen that initially the value of signal 22 is zero and the value of signal 24 is one. Signal 24 then drops to zero and shortly afterwards signal 22 rises to one. The period of time after signal 24 drops to zero and before signal 22 rises to one is shown as tl. The time tl is referred to as a "dead time".

After an interval of time, signal 22 then drops to zero, followed shortly afterwards by signal 24 rising to one. The time interval between these changes is shown as t2. The dead times tl and t2 may be the same or different.

The dead times tl and t2 are present in order to ensure that devices controlled by the signals 22 and 24 do not receive an "on" signal (value one) from both signals 22 and 24 at or near to the same time.

Figure 3 shows how the threshold values 11, 13, 15, 17 result in the switching signals 22 and 24. The threshold values 11, 13, 15, 17 are shown in relation to the ramping signal 7. As the value of the ramping signal 7 exceeds that of each of the threshold values 11, 13, 15, 17, the comparison signal from the comparators 10, 12, 14, 16 respectively changes value. The change in value of each of the comparators 10, 12, 14, 16 results in a change in value of one of the switching signals 22 or 24, as shown. Thus the values of the threshold values 11, 13, 15, 17 and the characteristics of the ramping signal 7 define the characteristics of the

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resulting switching signals 22 and 24.

The micro-controller 4 can also be used to alter the waveform of the signal output, as illustrated in figure 4.

The waveform of an output signal 26 from the logic circuit 18 is shown. The signal 26 initially has a value of zero and rises to a value of one. After a period of time a the signal 26 drops to zero. After a period of time b, the signal 26 rises to one. The signal thus has a wavelength of a + b. The periods of time a and b may be the same or different. These characteristics may be expressed in terms of a mark space ratio given as a/b.

The micro-controller 4 can be reprogrammed to alter the mark space ratios of the output signals from the logic circuit 18. This may be done by altering the threshold values generated by the DAC 8 and transmitted to the comparators 10, 12, 14 and 16, and/or altering the ramping signal generated by the ramp generator 6.

Preferably, the micro-controller 4 has a look-up table in its memory for convenient dead time programming.

Devices of the invention are particularly useful for product development as the switching signals may be dynamically changed by altering the settings of the micro controller 4 via the communications interface 20.

Also, a relatively low specification micro-controller may be used to construct the device of the invention whilst still achieving a relatively high accuracy switching signal. Thus the present invention allows for the relatively inexpensive manufacture of devices with accurate switching and timing signals.

Devices of the invention are particularly suitable for controlling power convertors, specifically for the control of a half-bridge for a DC to DC convertor. It is also applicable to three phase bridges or any other system which requires high resolution control.

Claims

1. An electronic device for generating a switching signal output comprising a micro-controller, a ramp generator, a digital to analogue convertor, a plurality of comparators and a logic circuit, the microcontroller being arranged to control the ramp generator to generate a ramping signal and to control the digital to analogue convertor to generate a threshold value signal for each of the comparators, each of the comparators being arranged for comparing the ramping signal with the threshold value signal so as to produce a comparison signal, and the logic circuit being arranged to receive each of the comparison signals and thereby produce at least one switching signal output.

152. A device according to claim 1 which is arranged to produce more than one switching signal.

3. A device according to claim 1 or 2 which is arranged to produce two switching signals.

4. A device according to claim 3 wherein the switching i signals alternate between a first value and a second value and the transition of one signal between the values is separated from the transition of the other signal between the values in the opposite sense by a dead time.

5. A device according to any preceding claim comprising four comparators.

6. A device according to any preceding claim wherein the micro-controller has a memory containing a look-up table for dead time programming.

7. A device according to any preceding claim further comprising a communications interface whereby the settings of the micro-controller may be altered to modify the characteristics of the at least one switching signal.

8. A device according to claim 7 wherein the characteristics comprise dead times and/or mark space ratios.

9. A device according to any preceding claim wherein the comparators are fast comparators.

10. A method of generating at least one switching signal comprising the steps of: providing a device comprising a micro-controller, a ramp generator, a digital to analogue convertor, a plurality of comparators and a logic circuit, controlling the ramp generator to generate a ramping signal, controlling the digital to analogue convertor to generate a threshold value signal to each of the comparators, 3 arranging for each of the comparators to compare the ramping signal with the threshold value signal so as to produce a comparison signal, arranging for the logic circuit to receive the comparison t signal from each of the comparators and thereby to produce a switching signal output.

11. A method according to claim 9 wherein the device is arranged to produce more than one switching signal.

12. A method according to claim 9 or 10 wherein the device is arranged to produce two switching signals.

13. A method according to claim 12 wherein the switching signals alternate between a first value and a second value and the transition of one signal between the values is separated from the transition of the other signal between the values in the opposite sense by a dead time.

14. A method according to any of claims 9 to 13 wherein the device comprises four comparators.

15. A method according to any of claims 9 to 14 wherein the microcontroller has a memory containing a look-up table for dead time programming.

16. A method according to any of claims 9 to 15 wherein the device further comprises a communications interface and the method further comprises the step of altering the settings of the micro-controller to thereby modify the characteristics of the at least one switching signal.

17. A method according to claim 16 wherein the characteristics comprise dead times and/or mark space ratios.

18. A method according to any of claims 10 to 18 wherein the comparators comprise fast comparators.

519. An electronic device substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

20. A method of generating a switching signal substantially as hereinbefore described with reference to and as shown in the accompanying drawings. 3

21. Any novel feature or combination of features disclosed herein.