Coded data generation or conversion – Analog to or from digital conversion – Digital to analog conversion
Reexamination Certificate
1999-04-22
2001-08-28
JeanPierre, Peguy (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Digital to analog conversion
C341S144000
Reexamination Certificate
active
06281827
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a signal conversion method, and more particularly to a method of converting digital signal to analog signal.
Conventional methods of converting digital signal to analog signal include the voltage (current) weighted method, the R-2R network method, and the pulse width modulation method.
Referring to
FIG. 1
, the voltage (current) weighted uses 8,4,2,1 binary weight ratios to achieve digital to analog conversion. According to this conversion method, we can obtain V
O
=V
R
×(A×2
3
+B×2
2
+C×2
1
+D×2
0
). The circuit for this voltage (current) weighted method is complicated. When the number of bits to be computed and the number of outputs are increased, the number of operational circuits must be relatively increased by a factor of 2
n
. Therefore, the cost of this method is high. Because the difference between MSB (the most significant bit) and LSB (the least significant bit) is large, the total accuracy is difficult to control the tolerance of MSB usually affects the tolerance and linearity of LSB a lot.
Referring to
FIG. 2
, the R-2R network method is similar to the voltage (current) weighted method. The difference of in the element value, as of element between MSB and LSB in the converting circuit according to R-2R network method is less significant, and can be relatively easily controlled, however the elements required for the converting circuit are complicated.
Referring to
FIGS. 3 and 4
, PWM (the pulse width modulation method) improves the drawbacks of low accuracy and complicated circuit structure, however it needs to run complicated comparison and switching actions. Because the frequency of actions is increased by a factor 2
n
, the drawbacks of high noise, high power consumption, low speed and poor linearity become inevitable.
SUMMARY OF THE INVENTION
It is one object of the present invention to provide a digital-to-analog conversion method which is simple, low cost, and highly efficient. It is another object of the present invention to provide a digital-to-analog conversion method, which achieves high linearity and high accuracy, and can directly process different bit lengths of or different encoding weights of codes. It is still another object of the present invention to provide a digital-to-analog conversion method which achieves high operation frequency but requires low power consumption. It is still another object of the present invention to provide a digital-to-analog conversion method, which is applicable for use to directly control any of a variety of circuits, and it is particularly suitable for multiple bit, multiple output applications.
The digital-to-analog conversion method of the present invention comprises the steps of:
(a) Processing at least one digital code;
(b) Inputting each of said at least one digital code to a single digital output port bit by bit for producing a respective analog signal;
(c) Multiplying a unit of time by a weight of encoding that represents the ongoing bit, so as to obtain an output period of time for the respective bit;
(d) Shifting to the next bit, then continuously repeating steps (b) and (c) till the last bit of each of said at least one digital code has been processed, and then continuously repeating the process.
According to the present invention, except for a reference voltage, the other elements produce almost no tolerance, therefore the amount of tolerance and the switching time can be excluded from calculation, and the accuracy is relatively high. For N bits operation, only an N bit register and/or latch are needed. The cost is therefore very low in comparison with conventional methods of which complexity and cost are increased by factor of 2
n
. The invention requires data shift only N times data shift. Therefore, linearity and speed can be much higher, and power consumption can be much lower in comparison with the conventional pulse width modulation solution. Furthermore, the process of the present invention is very simple, so that it can be achieved by only firmware or software solution by simply moving all same priority bits to output ports for a defined time. It is particularly suitable for applications of non-binary code, long code, and multi-output/input conversion, which can be achieved without significant extra cost or load. Analog output can control a high-speed power switching means to directly drive a power element such as an electromagnetic field speaker, electric heater, lamp, or DC motor.
REFERENCES:
patent: 3648275 (1972-03-01), Bower
patent: 4163287 (1979-07-01), Munter et al.
patent: 4835535 (1989-05-01), Shibayama et al.
patent: 4837573 (1989-06-01), Broks
patent: 5406284 (1995-04-01), Lin et al.
Jean-Pierre Peguy
Jeanglaude Jean Bruner
Onemore Inc.
Rabin & Champagne, P.C.
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