JPS60112326A - Analog/digital converter - Google Patents

Abstract

PURPOSE:To attain effectively the desired accuracy for a current source of a lamp voltage generator by comparing the input voltage with the lamp voltage given from the generator for broken line-shaped lamp voltage which contains switch groups and an integrator and extracting the digital output corresponding to each input voltage with the accuracy necessary for each register. CONSTITUTION:A switch S0 is opened at a time point t0 and a switch S1 is closed for a section of t1. The lamp voltage (y) rises up with a slope proportional to the courrent value I1 by an integration circuit (OP and C). A counter K1 starts counting with a clock CLK and produces the digital value corresponding to the lamp voltage value. the contents of a counter K are set to register groups L1-Ln when coincidence is obtained between the input voltages V1-Vn and the lamp voltage respectively. The switch S1 is opened at a time point (t0+t1) and the switch S2 is closed for a section of t2. The voltage (y) rises up in proportion to the value I2, and the counter K1 is shifted down by a shift signal SFT by an amount equivalent to the difference of weight between current values I1 and I2.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to an analog-to-digital converter (hereinafter referred to as an ADi converter) suitable for a device such as an X-ray eT device that needs to collect a large number of detector output data. ).

[Background of the invention]

As a multi-channel data acquisition circuit for X-ray CT equipment, etc.
There is a method using an integral type AD converter. All units share one ramp voltage generator, and by comparing the input voltage of each channel, counting is performed and output as a digital output. This method uses a straight line or a broken line as the lamp voltage generator. In particular, when a broken line is used to improve conversion accuracy (increase dynamic range), the accuracy of the current source in the lamp voltage generator must be improved, and the means for achieving this become complex. There was a point.

[Purpose of the invention]

An object of the present invention is to provide an analog ADf converter using a broken line lamp voltage generator to efficiently maintain the required accuracy of the current source in the lamp voltage generator.
There is a full range of digital converters to offer.

[Summary of the invention]

The present invention provides an integral method A for multi-channel data acquisition circuits.
Common to all channels in the Di converter.

It is characterized by theoretically analyzing the accuracy of the reference lamp voltage and efficiently achieving the required accuracy of the current source of the lamp voltage generator.

[Embodiments of the invention]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be explained below with reference to FIGS. 1 and 2. FIG. 1 is a circuit block diagram according to the present invention, and FIG. 2 is a signal waveform of each part. When switch SO is closed, lamp voltage ■. is reset to 0■. Time t. Then, switch SO is opened and only the section of switch 5 litl is closed. The lamp voltage y rises at a slope proportional to the current value 1 by the integrating circuit (OF and C). At this time, since the gate signal (G) becomes the u1'' level at the same time, the counter Kt starts inverse counting from 8 based on the clock (CLK).

The output of counter Kl generates a digital value corresponding to the value of the lamp voltage. Input voltage of each channel V11V
2. ...... When the lamp voltage matches y, the contents of the counter are changed to register groups Lx, L2,
......, it can be set to Lm.

At time to+t1, switch 81 is opened and switch 52 is opened.
Close only the it2 section. The lamp voltage y is the current value ■2
rises at a slope proportional to At this time, the shift signal (S
FT) 9% current source1. The difference in weight between and 2 is the same as the one full shift down on the counter. For example, Il is 1/
If 2 has a weight of 218 and 2 has a weight of 17216, the counter is shifted down by 1/22, which is the ratio of the two, or 2 bits. Time t(1+ tl +
At j2, the switch 82 is fully opened and only the section of the switch 53 it3 is closed. The lamp voltage y rises at a slope proportional to the current source 3. At this time, the shift signal (S F T
), the counter Klk is shifted down by the difference in weight between current sources (2) and (3).

The accuracy of these current sources will be analyzed with reference to FIGS. 3 and 4. FIG. 3 shows a portion of the lamp voltage generator of FIG. 1 extracted. FIG. 4 shows the output y of the lamp voltage generator. The output y of the dump voltage generator is at each divided time t1 + tz r t3, and the ramp voltage is Δyl, ΔV21 ly3, respectively.
It is assumed that there is a variation in As for the accuracy of each broken line voltage, yyB is a full school value without error. Further, each current source is represented by 1l=i+Δi, and can be represented by 1l=i+Δi. The accuracy of each broken line is determined by the variation in each current source. The broken lines of each section can be expressed as follows.

0 (t (t ly = i 1 t (1) tl
(t≦tl +tz ' Y=mli1t+YL (2
) tl+t2 (t≦t1+ tz + t3 y=m2
t1t+ )'2 (3) However, (1), (2),
In equation (3), the origin of the time axis was shifted for each valley fold line. Further, ml and m2 indicate the total ratio of the slope of each broken line, and indicate the number of blocks of the current source in FIG. 3. That is, B1
= 1, B2 = m11, B 3 = m 2
Get 1 hard.

(1), (2), (3) Equation s'/1 + y2
Add +73.

Yt-i+Δi) tl :i t1+Δitly2
=ml(i+Δi) tz +y1= (mlt2
+ 11) i+Δi(mth+tl)y3=
m2 (1+Δ1)t3+y2= (m2130m1
t2+tll i+Δi (m2 t3+m1t2+t
) To calculate the variation of each broken line, Δyl=Δitl Δy2 =Δi (mlt2+tt) ΔYs”Δi ([2t,, -1−ml t2+ t
l ) Tona 9. KIjK of the voltage w at each time is expressed as follows.

Rearranging equations (4), (5), and (6) gives degrees.

If we try to improve the n2 hit accuracy and the n hit accuracy, we can put it as follows, t3=α2”l * t2−αlt
Letting l, α = main - v' (9) 1mIX2'1 2 + 11 ten n3 2m9 α - (10) m2 x 21'1 each 112 bit precision [%nl bit precision only = 1/16.1/2 "l=1/4.m1=4.m
If we solve equations (9) and (10) with 2=16, we get α1=-
- 17'2 town to be improved, Calculate 1/2"l by H1", then use the circuit to solve equations (9) and [10), α5 and α2, that is, % tl + t2 Htl. Calculate the entire time. This circuit can be constructed using conventional techniques.

Also, the output of this circuit is %Switch group 81 in FIG.
2. You can connect to S3.

〔Effect of the invention〕

According to the present invention, the required accuracy of the current source of the lamp voltage generator using a broken line can be realized with full efficiency, and the integral type ADi converter for multi-channel data collection can be implemented at high speed and with high accuracy.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an integral type AD converter for multi-channel data collection according to the invention, Fig. 2 is a signal waveform diagram of each part, and Fig. 3 is a block diagram of a lamp voltage generator. Figure 4 is a diagram showing the shape of the lamp voltage, and Figure 5 is a diagram showing the control circuit that allocates time to obtain the required accuracy for each broken line. Agent Patent Attorney Akio Takahashi No. 1 Fig. ri θ Fu Z Fig. fρ 3 Fig.

Claims (1)

[Claims] 1. In an integral type analog-to-digital converter that collects data in parallel for each channel, a plurality of constant current sources maintained at a certain precision, a group of switches for sequentially switching them, and an integral a linear lamp voltage generator having a linear lamp voltage generator, a comparator group that compares the lamp voltage from the lamp voltage generator with the input voltage, and a comparator group that compares the input voltage with the lamp voltage from the lamp voltage generator, and a comparator group that compares the input voltage with the lamp voltage from the linear lamp voltage generator, and a set of counters that shift down based on the weights of and count at a constant clock, and a set of registers that sets the entire contents of the counter at a time corresponding to the input voltage according to the output of the comparator group. It consists of a time generating circuit that generates the opening and closing times of the switch group based on the required accuracy of each broken line of the above-mentioned broken line voltage, and a digital output complete register corresponding to each input voltage is extracted with the necessary accuracy. analog-to-digital converter. 2. In the analog-to-digital converter according to claim 1, the accuracy of the three broken lines is improved by the accuracy of one broken line by k n 1 bits and n2 pits of the other two broken lines. An analog-to-digital converter characterized in that it has a time generating circuit that sequentially changes the opening and closing times of a group of switches when desired.