JPS61244129A - Transmission system for analog signal - Google Patents

Abstract

PURPOSE:To send out an analog signal with high resolution by using an inexpensive DAC which has a small number of input bits by calculating a large and a small digital signal value which are closest to an analog signal value to be sent out according to the number of input bits of the DAC and supplying them to the DAC alternately. CONSTITUTION:A fixed memory ROM 2, a variable memory RAM 3, timer TIMs 4 and 5, and interface I/Fs 6 and 7 are arranged at the periphery of a CPU 1 such as a microprocessor and connected by a bus; the I/F 6 is supplied with input data D1 and the I/F 7 sends output data with a digital signal (d). Then, the data is converted by the DAC 8 into an analog signal (a), which is averaged by an averaging circuit 9 using an integration circuit, etc., and sent out as an analog signal a0. In this case, the DAC 8 is supplied with digital signals of the large and small values which are closest to the analog value to be sent out alternately as a specific duty ratio according to the number of input bits.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for converting a digital signal into an analog signal using a digital-to-analog converter and transmitting the analog signal.

[Conventional technology]

When converting a digital signal into an analog signal and sending it out, a digital-to-analog converter (hereinafter referred to as DAC) is generally used.
In this case, a DAC with the number of input bits corresponding to this resolution is used, depending on how finely it is necessary to show the changes in the analog signal to be sent.
is used.

[Problem that the invention seeks to solve]

However, in order to improve the resolution of analog signals with high accuracy, it is necessary to use a DAC with a correspondingly large number of input bits, resulting in the problem that the DAC becomes expensive.

[Means for solving problems]

In order to solve the above-mentioned problem, the present invention is constructed by the following means.

That is, in the above method, the digital signal values of the large value and small value that are closest to the analog signal value to be sent are determined according to the number of input bits of the DAC, and these digital signal values of the large value and small value are alternately transmitted. To DA
C, the output of this DAC is averaged and sent as an analog signal, and the value of this analog signal becomes the analog signal value to be sent.As a duty ratio, a digital signal with a large value and a small value is given to the DAC. There is.

[For production]

Therefore, by inserting an integrating circuit etc. on the output side of the DAC,
By averaging the output of the AC, the analog signal value to be sent out can be obtained, and the DAC also has a predetermined digital signal that is closest to the analog value to be sent out, and has a large value or a small value, depending on the number of input bits. It is sufficient if they are given alternately as the duty ratio.

[Act 1! Example A] Hereinafter, the present invention will be described in detail with reference to figures showing examples.

Figure 2 shows a block diagram, centered around a processor such as a microprocessor (hereinafter referred to as CPU) 1, a fixed memory (hereinafter referred to as ROM) 2, and a variable memory (hereinafter referred to as RAM).
) 3, a timer (hereinafter referred to as TIM) 4.5 and interfaces (hereinafter referred to as I/'F) 6 and 7 are arranged around the circuit, and these are connected by a bus bar, and input data Di is given to I/F6. The output data is sent from the I/F 7 as a digital signal d, which is converted into an analog signal by the DAC 8, which is averaged by an averaging circuit 9 using an integrating circuit, etc., and converted into an analog signal. The barrel.

It is designed to be sent out in a closed format.

At this point, CPU1 executes the instructions in ROM2,
Control and calculation are performed while accessing the necessary data to RAM3, and the value of analog signal a0 is obtained by calculation based on input data D1, and this is sent out using digital signal d. For example, if the number of input bits is 4 bits, the number of input bits is insufficient to realize the resolution required for the analog signal a0.

Therefore, the value dn of the digital signal d given to the input of the DAC 8, and the value & of the analog signal a obtained therefrom. The relationship with is as shown in Figure 3, and dn=15 is a
If n is 100 yen, when drh=7, a n= 4
6.7%, when dn=8, 1n=53.3%,
It is not possible to obtain an analog signal an of an=50%.

Therefore, to obtain an=50chi, one period is required as shown in FIG. is divided by period X and period y, and in period
In the period y, the digital signal value dl+, which is closest to atl=50% and has a large value, is given to AC8, (8=
53.3%) to I) AC8, and each x:y=
By repeating alternately with a duty ratio of 1:1, the corresponding analog signals 11 and 2 are averaged by the averaging circuit 9, and the average value a0 becomes 50.

That is, when to=100%, X"-y-50
%, and ao is the area average value of each period x, y, so 46.7 X − + 53.3 x rent i = 50 (%
)...(1), and di corresponding to &11&i+□
By determining ldl+1 according to the number of input bits of the DAC 8 and repeating these with a duty ratio such that the average value a0 of &i and ILi+1 becomes a desired analog signal value, an analog signal a0 of the value to be sent can be obtained.

Therefore, by generalizing equation (1), the following equation holds true.

)...(2) x+y=100 When X and y are determined from equation (2), the following equation is obtained.

)'=100-x ・・・(
4) Therefore, for example, if a0=51, dl
-46.7chi, a, , = 53.3%, and (from formula 35, each digital signal value dl.

It is sufficient to alternately apply the signals to d1+1t-DAC8.

FIG. 1 is a flowchart of the control and calculation status by the CPU 1, in which each part is initialized by 'Initialize' 101, and then 'Initialize' is performed based on the input data D1.
Perform a0 operation "102" and accordingly "dl,
In addition to performing “111 to find di+1”, these d
'X according to equation (3) using l, d1+1 and ao
Perform operation "112," TIM4 hex set l11
21 and to TIM5. After performing the set "122", perform the "TIM4.5 start °°123".

Next, perform “dl sending” 131 from I/F 7,
If “TIM4 time up?” 132 is Y (YES), perform ``dl+, send'' 141, and TIM5
Time up? According to Y of ``142, input data ``Di
change? ” 151 is checked, and while this is N (No), steps 121 and subsequent steps are repeated, whereas if step 151 is Y, steps 102 and subsequent steps are repeated.

In step 111, the relationship shown in FIG. 3 is stored as a table in the ROM 2 or RAM 3 and calculated using this table, or by successive comparison of each input digital value corresponding to the number of input pits of the DAC 8 with 10. And it is sufficient.

Therefore, the digital input value dn in FIG. 3 and the corresponding analog output value &. You can also send intermediate values other than
It is sufficient to use an inexpensive DAC 8 with a small number of input bits.

Alternatively, TIM4 and TIM5 may be configured by software using CPU1 and RAM3, and the period y is also calculated to configure TIM4 and TIM5.
The same effect can be obtained by setting this to 5 and starting in response to Y in step 132.

Further, in addition to an integrating circuit using a resistor and a capacitor, the averaging circuit 9 may also use an integrator using an operational amplifier, or a low-frequency F-wave device, etc.
The same effect can be achieved by constructing equivalent circuits using various arithmetic circuits and logic circuits without using
Various modifications can be made, such as setting 21 to "y set'°.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, a high-resolution analog signal can be sent using an inexpensive AC with a small number of input bits, so it can be used for various applications in which a digital signal is converted into an analog signal using a DAC and then sent. Remarkable effects can be obtained.

[Brief explanation of drawings]

The figures show an embodiment of the present invention, in which Figure 1 is a flowchart of control and calculation status, Figure 2 is a block diagram, and Figure 3 is a D
FIG. 4 is a diagram showing the relationship between the input value and the output value of the AC, and FIG. 4 is a diagram showing the transmission status of the digital signal. 1...CPU (processor), 4.5...T
IM (timer), 8...DAC (digital
analog converter), 9...averaging circuit.

Claims (1)

[Claims] In a method in which a digital signal is converted into an analog signal by a digital-to-analog converter and sent out, a digital signal value that is closest to the analog signal value to be sent out according to the number of input bits of the digital-to-analog converter, and has a large value or a small value. , and alternately apply these large value and small value digital signals to the digital-to-analog converter, average the output of the converter to make an analog signal to be sent out, and the value of the analog signal is equal to the analog signal. An analog signal sending system characterized in that the digital signals of the large value and the small value are given to the digital-to-analog converter as duty ratios serving as signal values.