JPH01295530A - Ad conversion system - Google Patents

Abstract

PURPOSE:To attain AD conversion without offset by using a digital signal processing section so as to detect the offset and to correct it based on an input signal during a period of no input to the AD converter and an output signal of the AD converter of the period. CONSTITUTION:The AD converter applies the 1st conversion at a time t=1, and an analog signal V1 is converted into a digital signal C1 in this case. Then the 2nd conversion is applied at a time t=2 and an analog signal V2 in converted into a digital signal C2. The cycle above is repeated at t=m, that is, at the end of offset detecting period. When the offset detection period is finished at t=m, an offset is calculated and detected in a digital signal processing section. Then offset correction AD conversion is started based on the detected offset and the processing is continued till the signal processing system reaches the state of the end of AD conversion. Thus, the AD conversion independently of the offset of the AD converter is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to an AD conversion method in a signal processing system including an AD converter and a digital signal processing section.

<Prior Art> FIG. 4 shows an example of the configuration of a signal processing system including an AD converter and a digital signal processing section. Analog input signal 404
is converted into a digital signal 405 by the AD converter 401, and the digital signal 405 is converted into a digital signal 405 by the digital signal processing unit 402.
After being processed, it is sent to the output unit 403. Output section 40
In 3, either a digital signal or an analog signal,
Or both are output depending on the purpose of this signal processing system.

Now, Table 1 shows an example of input/output correspondence of the AD converter 401.

Table 1 In the example of Table 1, o, oov to 5. OOV analog signal 000...o o (J2) ~ 111...+I
+(2) is an AD conversion that digitizes n bits in 2 steps, and theoretically, o and oov are OOO-00.
0(2), 500v is 111...I I 1(2)
Convert to Here, (2) indicates that this number is a binary number. However, as shown in Table 1, the actual AD
A converter outputs a value with a slight deviation (offset) from the theoretical value due to problems such as the accuracy of its constituent elements (capacitors, resistors, etc.). In the example in Table 1, the offset is +
Example 2 is shown.

Offset is one of the items that indicate the performance of an AD converter, and ideally it is required to be 0, so how to reduce this offset is one of the points in AD converter design. , many efforts have been made in the past.

<Problems to be Solved by the Invention> In a signal processing system having an AD converter and a digital signal processing unit, it is extremely difficult to perform conversion without offset of the AD converter using conventional technology. was there.

<Means and operations for solving the problem> In order to solve the above-mentioned problems, in the present invention, the input signal of the period when the input signal targeted by the signal processing system is not input to the AD converter, and the AD conversion of this period. The offset is detected in the digital signal processing section based on the output signal of the device, and the offset is corrected for the output signal of the AD converter for the target input signal, and the offset is taken into the digital signal processing section. This enables AD conversion without

<Example> An example of the present invention will be described based on FIGS. 1 to 3. It is assumed that the AD converter performs conversion according to the correspondence shown in Table 1 for convenience.

Figure @1 is a flowchart of this embodiment.

The AD converter starts AD conversion for offset detection before the input signal targeted by the signal processing system actually comes in. Offset detection is performed during a fixed period of time, but the period for offset detection should be set in consideration of the frequency of noise superimposed on the input signal, and should be set to a length that does not cause problems in actual use of the signal processing device. do it. In the flowchart, m corresponds to this detection period,
The relationship m=offset detection period/AD conversion period is satisfied.

The AD converter performs the first conversion at time 1=1, and at this time, as shown in FIGS. 2 and 3, the analog signal value V
(1) is converted to the digital signal value C(1+. Here, it should be noted that as shown in Table 1, theoretically Vf1
+= C that should correspond to 2.5 V (1+ is 100...
000(2), but in reality it is 100 plus the offset (=+2) of this AD converter...OI 0
(2) is output as Cm. Next, at time t=2, 2
A second conversion is performed, and the analog signal value v(2) is converted into a digital signal value C(2). This cycle is t=
This is repeated until m, that is, the end of the offset detection period.

During the offset detection period, offset correction is not performed on the AD converter, so as shown in Figures 2 and 3, the AD conversion results are as if the input level were a slightly higher voltage value. becomes.

Now, when the offset detection period ends at t=m, the offset is calculated and detected by Equation 15 in the digital signal processing section. There are many ways to calculate the offset, but in this example, t=m and t=
'm+I according to the above formula.

Next, offset correction AD conversion is started based on this detected offset. At time t = m+1,
v(m+1 is C(m+1)-offset=100...
・OI 0(2)-2= + 00...OO0(2)
The offset is corrected and converted as follows, and AD conversion is continued in the same manner as t=m+2,...
This continues until the signal processing system reaches the state where AD conversion is completed.

<Effects of the Invention> As described above in detail, the present invention enables AD conversion that is not related to the offset of the AD converter, and provides a significant effect in signal processing systems where offset is a problem.

[Brief Description of the Drawings] Fig. 1 is a flowchart of an embodiment of the present invention, Fig. 2 is an analog signal example diagram for explaining the embodiment, and Fig. 3 is a diagram after AD conversion for explaining the embodiment. FIG. 4 is a diagram showing an example of the configuration of a signal processing system having an AD converter and a digital signal processing section. Explanation of symbols 401: AD converter, 402: Digital signal processing unit, 4
03: Output section, 404: Analog signal, 405: Digital signal. Agent Patent Attorney Takeshi Sugiyama (and 1 other person) Compilation I

Claims (1)

[Claims] 1. In a system that includes an AD converter and a digital signal processing unit that processes digital signals, the digital signal value that is theoretically associated with the analog signal value that is input to the AD converter and the actual AD conversion The digital signal processing section detects the difference with the digital signal value output from the device (AD converter offset), and corrects it while performing the AD converter offset.
An AD conversion method characterized by performing conversion.