JP2001060856A - Method and device for outputting signal with modulated pulse width - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate a signal with a modulated pulse width, which is provided with improved resolution and a comparatively wide value range by outputting a signal width in accordance with a pulse duty factor to be previously set. SOLUTION: When the pulse duty factor TV between a high level signal continuing time T-H and a low level signal duration T-L is >=50%, a minimum duration T-min to be kept between two continuous signal edges is defined as the minimum permission width of a low level signal or a minimum permission continuing time. The high level signal duration T-H is outputted as the signal in accordance with the pulse duty factor TV to be previously set. When TV is smaller than 50%, T-min is outputted as the minimum permission width of the high level signal or a minimum permission duration. Then the low level signal duration T-L is outputted in accordance with the pulse duty factor TV to be previously set.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for outputting a pulse width modulated signal (PWM signal) having a high level signal of a first width and a low level signal of a second width.

[0002]

2. Description of the Related Art In many application cases, target value setting,
It is necessary to supply an analog value using a microcontroller, for example for the current target value of the output stage. For such analog values, the best possible smoothing or filtering is required at the same time as the dynamic high-quality variability. Another example is a digital controller, which requires a digital-to-analog converter to output the calculated manipulated variable to an analog control section. For this purpose, pulse width modulators are often used, which output the pulse width in proportion to the digital setting, which, after low-pass filtering, corresponds to the analog voltage value. I do. Such a pulse width modulator has proven to be extremely inexpensive and advantageous. For example, it is possible to use a microcomputer with a pulse width output, or to incorporate the required digital electronics into the ASIC. Therefore, the additional cost for a digital-to-analog converter often comes only from the cost of an RC element that can be used as a simple low-pass filter. Such a digital-to-analog converter has better linearity and monotonicity.

However, it has been found that the conventional pulse width modulator used as a digital-to-analog converter has a relatively slow dynamic characteristic and a relatively low output frequency spectrum.

In order to eliminate this drawback, the periodicals "Aut"
omatisierungstechnik "41 (1993) 11, 428-43
On page 2 it is proposed to use a so-called pulse count modulator instead of a pulse width modulator. The advantage of using a pulse count modulator here is that when the resolution of the timer is equal, compared to pulse width modulation,
It is stated that a clearly higher output frequency spectrum is possible as well as a quicker change of the target value. Furthermore, smaller and more cost-effective filter stages can be used compared to pulse width modulation.
However, a disadvantage of pulse count modulation is that it requires dedicated hardware or a specially designed calculation algorithm, which increases the procurement cost or operating cost of the pulse count modulator.

[0005] Currently available microcomputers include high resolution PWM signals (eg, 20M per event).
Hz timer, 50 ns resolution), there are intelligent or programmable peripheral units which have a lower limit on the interval between two consecutive signal edges, for example limited to 10 μs. Often has restrictions. This is based on reload time or calculation time.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to form a pulse-width modulated signal having improved resolution and a relatively wide range over conventional signals,
The aim is to make the frequency of this pulse width modulated signal as high as possible so that the subsequent filter stages can be designed with the highest possible cut-off frequency. Here, in particular, it must be possible to vary the output frequency itself.

[0007]

According to the present invention, there is provided a method for outputting a pulse width modulated signal having a high level signal having a first width and a low level signal having a second width. The width of the high-level signal in the first operating state, the width of the low-level signal in the second operating state,
A method of outputting a pulse width modulated signal characterized by outputting according to a pulse duty factor to be set in advance and / or performing subsequent processing, and a width of a high level signal according to a pulse duty factor to be set in advance Output and / or subsequent processing, and the width of the low level signal is output and / or according to a pulse duty factor to be set in advance.
Alternatively, there is provided a device for outputting a pulse-width-modulated signal, characterized in that means for switching between a second operating state to be processed subsequently are provided.

[0008]

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a pulse width which has an improved resolution within a desired value range compared to conventional signals, and has a higher signal frequency than comparable comparable solutions. A modulated signal can be formed. Thus, for example, subsequent filter stages can be designed with a higher cutoff frequency.

[0009] Advantageous embodiments of the method or the device according to the invention are described in the dependent claims.

The pulse duty factor between the high level signal and the low level signal of the pulse width modulated signal is 50.
%, The minimum allowable signal level width is defined for the high level signal and the low level signal is output or post-processed as a pulse width modulated signal, and if the pulse duty factor is greater than 50%. Advantageously defines the minimum allowable signal level width with respect to the low level signal and outputs or further processes the high level signal as a pulse width modulated signal. Here, the pulse duty factor is a time ratio between the high-level signal and the low-level signal. When the pulse duty factor is smaller than 50%, the low-level signal is less than half of the entire signal period. It means big.

Advantageously, in the present invention, a minimum pulse duty factor of, for example, 10% and a maximum pulse duty factor of, for example, 90% are preset. This avoids an endlessly low output frequency which occurs with a pulse duty factor of approximately 0 or 100%.

It has furthermore been found advantageous to switch between the operating states using hysteresis.

The present invention will be further described with reference to the drawings.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a pulse width modulator, a minimum spacing between two consecutive signal edges must be observed for reload or calculation time. Corresponding duration T_min
For a typical pulse width modulated signal in FIG.
Is shown in Here, the duration T of the high-level signal
The pulse duty factor TV between _H and the duration T_L of the low level signal is greater than 50%. These two
By two durations or widths T_H, T_L,
An output signal period T_P of the pulse-width modulated signal is obtained. Here, the duration T_L of the low level signal is the minimum duration T_L between two consecutive signal edges to be protected.
equal to min. By adjusting the duration of the low-level signal T_L to the value T_min, the frequency fp (reciprocal of the period T_P) of the pulse-width-modulated signal is maximized without compromising the availability of the pulse-width-modulated signal. can do. In this state, the duration T_H is output as a signal according to the pulse duty factor to be set in advance. There is no problem because this duration is greater than T_min (TV> 50%).

By shortening the duration T_H of the high-level signal, the period T_P of the pulse-width-modulated signal can be further shortened, because the duration T_H of the high-level signal is determined between two consecutive signal edges. Is performed until it becomes equal to the minimum interval T_min. This state is shown in FIG.
B. In this state, it can be seen that the period T_P of the pulse width modulated signal is the minimum, that is, the frequency f of this signal takes the value f _max . The pulse duty factor TV is 50% in this state.

To further reduce the pulse duty factor, the duration of the low level signal T_L is increased. Here, T_min is defined or output as a minimum allowable high level duration or high time (FIG. 1).
C). Here, the duration T_L is output as a signal according to a pulse duty factor to be set in advance. The duration T_L is greater than T_min (TV
<50%), so there is no problem.

What is important is that when the pulse duty factor of 50% is reached, two states, namely, "output of a high-level signal according to the pulse duty factor to be set in advance" and "output of the pulse duty factor to be set in advance" And output of a corresponding low-level signal. Switching between the two states can be performed by suitable control means, for example, a microcontroller to which the pulse width modulator belongs. Here it is possible in some cases to incorporate a small hysteresis. The corresponding characteristic curve is shown in FIG. 2 and shows the output frequency f of the pulse-width-modulated signal.
Are plotted against the pulse duty factor TV. It can be seen that at a pulse duty factor of 50%, the characteristic curve shows a continuous course, so that no jump occurs. The output frequency f has a maximum value when the pulse duty factor TV is 50%, as shown in FIG. An output signal which is optimally adapted, i.e. as high as possible, is always obtained over the entire range of pulse duty factor which can be advantageously set (for example, when limited by a pulse duty factor of 10% or 90%). . The output frequency signal thus optimized allows subsequent filter stages to be designed with a correspondingly high cut-off frequency.

By using the method described above, the highest possible frequency can be achieved in each case using standard hardware (thus with minimum filter cost despite maximum dynamic performance). Can be achieved. Further optimization is not possible without additional hardware (eg pulse count modulation, complex filters, higher frequencies).

The method of the present invention will be described again with reference to the flowchart of FIG. In a first step 101, it is determined whether the pulse duty factor is greater than or equal to 50% using suitable control means not shown here. If so, go to step 102, where T_min is defined as the minimum allowable width or minimum allowable duration of the low level signal of the pulse width modulated signal. In step 103, the duration of the high-level signal is output as a signal according to the pulse duty factor to be set in advance.

On the other hand, if it is detected in step 101 that the pulse duty factor is smaller than 50%, the process proceeds to step 104, where T_min is
It is output as the minimum allowable width or minimum allowable duration of the high-level signal. Next, in step 105, the duration of the low-level signal is output according to the pulse duty factor to be set in advance.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating various states of a pulse width modulated signal.

FIG. 2 is a schematic diagram of a typical characteristic curve of a pulse width modulator operated according to the present invention, plotting output frequency against pulse duty factor.

FIG. 3 is a flowchart further illustrating the method of the present invention.

[Explanation of symbols]

 T_min Minimum interval between two consecutive signal edges T_H Duration of high-level signal T_L Duration of low-level signal TV Pulse duty factor T_P period

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Josef Newald Germany Germany Schuttgart Banzhardenstrasse 89

Claims (5)

[Claims] 1. A method for outputting a pulse width modulated signal having a high level signal of a first width and a low level signal of a second width, wherein the width of the high level signal is reduced in a first operating state. And second
In the operating state of, the width of the low-level signal is output according to the pulse duty factor to be set in advance.
And / or a subsequent process for outputting a pulse width modulated signal. 2. When the pulse duty factor between the high-level signal and the low-level signal is smaller than 50%, the minimum allowable signal level width is defined for the high-level signal, and the low-level signal is set in advance. Output according to the duty factor. If the pulse duty factor is greater than 50%, the minimum allowable signal level width is defined for the low level signal, and the width of the high level signal is output as the pulse duty factor to be set in advance. The method of claim 1, wherein 3. The method according to claim 2, wherein a minimum pulse duty factor of, for example, 10% and / or a maximum pulse duty factor of, for example, 90% are preset. 4. An apparatus for outputting a pulse-width-modulated signal having a high-level signal having a first width and a low-level signal having a second width, wherein the pulse width of the high-level signal is set in advance. Means for switching between a first operating state in which output and / or subsequent processing is performed according to a factor and a second operating state in which output and / or subsequent processing is performed according to a pulse duty factor whose width of a low-level signal is to be set in advance. A device for outputting a pulse width modulated signal. 5. The apparatus according to claim 4, wherein the switching of each operation state is performed using hysteresis.