Analog-to-digital conversion method and device

Details Analog-to-digital conversion method and device Analog-to-digital conversion method and device

2003-04-21

2004-08-03

Young, Brian (Department: 2819)

Coded data generation or conversion

Analog to or from digital conversion

Analog to digital conversion

C341S118000

Reexamination Certificate

active

06771202

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an analog-to-digital (A/D) conversion method and device for converting an analog input signal into numerical data using a pulse delay circuit that has a plurality of delay units, which delay and transmit a pulse signal, connected in series with one another.
2. Description of the Related Art
In the past, A/D conversion devices known as types of A/D conversion devices that provides high-resolution digital data despite a simple configuration include a pulse delay circuit that has a plurality of delay units, which are realized with various kinds of gate circuits, connected annularly. In the A/D conversion device, an analog input signal, that is an object of A/D conversion, is transmitted as a supply voltage to the pulse delay circuit. At the same time, a transmission pulse signal is applied to the pulse delay circuit. Consequently, the pulse signal is circulated through the pulse delay circuit at a speed dependent on the delay time of the delay units. The number of delay units in the pulse delay circuit through which the pulse signal passes within a predetermined sampling time during the circulation of the pulse signal is counted. Thus, the analog input signal is converted to numerical data (refer to, for example, Japanese Unexamined Patent Application Publication No. 5-259907).
The A/D conversion device utilizes the fact that a delay time to be given by the delay units varies depending on a supply voltage. Since an analog input signal is transmitted as a supply voltage to the delay units included in the pulse delay circuit, the speed at which a pulse signal circulates through the pulse delay circuit is changed with the analog input signal. The moving speed is measured by counting the number of delay units through which the pulse signal has pass through within the predetermined sampling time. The result of the measurement (count value) is provided as numerical data resulting from A/D conversion.
According to the A/D conversion device, a voltage resolution to be expressed by resultant numerical data can be determined with a delay time given by one stage of a delay unit included in the pulse delay circuit and a sampling time required for A/D conversion. In order to increase the voltage resolution expressed by the numerical data, the delay time to be given by one stage of a delay unit is shortened or the sampling time is extended. Consequently, an A/D conversion device capable of realizing high-precision A/D conversion can be provided inexpensively with a simple configuration.
However, in the foregoing A/D conversion device, the delay time to be given by one stage of a delay unit included in the pulse delay circuit is determined by a fineness level (a rule for CMOS design). The fineness level indicates how fine circuit elements (inverters or other gate circuits) included in each delay unit are. Even if an attempt is made to shorten a delay time of one stage of a delay unit included in the pulse delay circuit for the purpose of improving a resolution to be offered through A/D conversion, there are limitations.
Moreover, when, in the A/D conversion device, the sampling time required for A/D conversion is extended in order to improve a resolution to be offered through A/D conversion, and the A/D conversion device is employed in a system required to achieve high-speed A/D conversion at an A/D conversion speed ranging from, for example, several megahertz to several tens of megahertz, the system would suffer from insufficient speed. The system could not satisfy a requirement for high-speed A/D conversion.
The foregoing A/D conversion device is a so-called integrating type A/D conversion device. Produced digital data is a result of integration performed on a variable component of an analog input signal over a sampling time required for A/D conversion. Therefore, if the sampling time required for A/D conversion is extended in order to improve a resolution to be offered through A/D conversion, quantity of variation of the analog input signal cannot be reflected on the resultant digital data. The A/D conversion device cannot be employed in a system requested to achieve high-speed A/D conversion.
Therefore, a system that requires the speed and precision of A/D conversion conventionally employs a successive approximation type A/D conversion device or a parallel type A/D conversion device (also called a flash type A/D conversion device). The successive approximation type A/D conversion device can achieve A/D conversion at a higher speed than the aforesaid integrating type A/D conversion device can. The parallel type A/D conversion device can achieve A/D conversion instantaneously.
In order to improve the resolution offered through A/D conversion by the successive approximation type A/D conversion device or parallel type A/D conversion device, numerous reference voltages must be produced according to the required resolution. Therefore, a system that requires the speed and precision of A/D conversion must employ an expensive A/D conversion device having a complex configuration. This invites an increase in the cost of the entire system.
SUMMARY OF THE INVENTION
The present invention attempts to solve the foregoing problem. Accordingly, an object of the present invention is to provide an A/D conversion method for converting an analog signal into digital data at high speed with high precision using an A/D conversion device that can be realized inexpensively with a simple configuration, and the A/D conversion device.
According to an A/D conversion method in which a first embodiment of the present invention is implemented in order to accomplish the object, a delay time to be given by delay units constituting a pulse delay circuit is changed with an analog input signal. A pulse signal is applied to the pulse delay circuit and transferred within the pulse delay circuit. The position of the pulse signal within the pulse delay circuit is numerically expressed at a plurality of different timings. The results of the numerical expression are summated in order to produce numerical data representing the analog input signal.
According to the A/D conversion method of the present invention, similarly to the method implemented in the aforesaid conventional A/D conversion device, the pulse delay circuit is used to convert the analog input signal into numerical data. During the A/D conversion, the position of the pulse signal within the pulse delay circuit is not numerically expressed at the timing that a predetermined time has elapsed since the pulse signal is applied to the pulse delay circuit, but numerically expressed at a plurality of different timings. The results of the numerical expression are summated in order to produce numerical data.
Herein, the number of bits constituting numerical data that results from the numerical expression of the position of the pulse signal within the pulse delay circuit is n, and the number of numerical data items produced at the plurality of different timings is m. In this case, the number of bits constituting numerical data produced by the A/D conversion method of the present invention is provided as n+log
2
m.
The numerical data n+log
2
m bits long corresponds to an average of numerical data items produced at the plurality of different timings. Consequently, a voltage resolution expressed by final numerical data is higher than that expressed by numerical data produced according to the conventional method.
According to the A/D conversion method of the present invention, the action of numerically expressing the position of the pulse signal within the pulse delay circuit is not merely performed a plurality of times. The plurality of timings at which the numerical expression is performed is differentiated from one another. The time required for A/D conversion is not longer than the one required according to the conventional method. A/D conversion can be achieved with high precision by taking the same time as the one required by the conventional method. Moreover, if a voltage resolution

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