JP2826403B2 - Receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver for use in a hybrid communication system in which, for example, a high-frequency signal representing communication information is superimposed on a low-frequency signal representing a measured value and transmitted. More specifically, the present invention relates to a receiver capable of separately extracting a low-frequency signal and a high-frequency signal from a received superimposed signal.

[0002]

2. Description of the Related Art In a recent process control system used in the field of industrial instruments, a high-frequency signal representing communication information is superimposed on a low-frequency signal representing a measured value and transmitted. I have. In this specification, a signal in which a high-frequency signal (communication information) is superimposed on a low-frequency signal (measurement signal) is referred to as a hybrid communication signal. An example will be described. The actuator attached to the plant side measures, for example, the flow rate of the liquid flowing through the pipe, and replaces the measured value indicating the flow rate with, for example, a current value of 4 to 20 mA.
4 mA means a flow rate of 0, and 20 mA means a flow rate value of 100% of the measured value of the actuator in the measurement range. Then, this is transmitted to a central control device installed at a remote place via a transmission line.

[0003] In the past, actuators simply transmit only measured values, but recent actuators have a built-in microcomputer and transmit not only measured values but also various kinds of communication information in 4-20 mA (measured values). Value). The communication information includes, for example, measurement range information of the actuator itself, information of a response to the communication information transmitted from the central control device, and the like.

FIG. 6 is a diagram showing a waveform of a hybrid communication signal on which communication information is superimposed as described above. In the figure, I _L is a low-frequency signal indicating a measured value (for example, a flow rate).
This is a value between 20 mA. On the other hand, i _H is a high-frequency communication signal representing communication information, and has a waveform i shown in FIG.
_H forms information by the presence or absence of a pulse. A signal subjected to various types of modulation such as ASK modulation and FSK modulation is used as a high-frequency signal representing communication information.

The central control unit is provided with a receiving device to receive the transmitted waveform as shown in FIG. This receiver separates and extracts the low frequency signal I _L and the high frequency signal i _H from the introduced waveform of FIG. Then, the high-frequency signal i _H is further demodulated to reproduce communication information. The central control device, which is based on a computer, calculates a control amount based on the measured value and the communication information and sends a control signal to the process side.

FIG. 7 is a diagram showing a configuration example of a conventional receiving device provided on the central control device side. 7 introduces a hybrid communication signal S1 as shown in FIG. 6 from the process side (not shown) via the transmission line 1. And an HPF (high pass filter) 3 composed of an analog circuit.
And a low-frequency signal component (measured value) and a high-frequency signal component (communication information component) by an LPF (low pass filter) 5. Further, the communication signal i _H is applied to the comparator 7 with hysteresis, and a pulse signal S3 that forms a pulse edge when the communication signal i _H crosses zero is created. The pulse signal S3 is applied to a demodulator (not shown), and communication information is reproduced from the time series of the pulse width of the pulse signal S3.

[0007]

In recent years, in the field of the electronics industry, many parts of electronic circuits have been integrated into ICs to reduce the size, performance and cost of products. In particular, if the signal handled by the circuit is a digital signal and the electronic circuit can be replaced with a digital IC, the function and performance of the product can be dramatically improved.

The reason is that, when digitized, subsequent signal processing can be performed by a microprocessor, so that various arithmetic processing can be performed. As a result, a product with abundant functions can be realized. Furthermore, the operation using the microprocessor can be freely changed in software without changing the hardware, so that in terms of function flexibility, compared to the conventional analog operation principle device. It is advantageous.

In view of the above, when FIG. 7 is viewed, it is preferable that the circuit shown in FIG. 7 constituted by analog circuit elements be constituted by a digital circuit. However, if the conventional circuit of FIG. 7 is to be replaced with a digital circuit as it is, HPF and L
Two digital filters of PF are required. An analog circuit filter could be easily configured with a resistor and a capacitor.However, a digital circuit filter generally required a multiplier, causing a problem that required a relatively large circuit scale or computational power. I do.

An object of the present invention is to provide a receiving apparatus capable of separating a low frequency component and a high frequency component from an introduced hybrid communication signal by using only one digital filter having a relatively small circuit scale or a relatively small computing capability. is there.

[0011]

SUMMARY OF THE INVENTION The present invention is an apparatus for receiving a so-called hybrid communication signal in which a high-frequency signal is superimposed on a low-frequency signal and separating and extracting a low-frequency signal component and a high-frequency signal component. in samples the instantaneous value of the hybrid communication signal, which was introduced and AD converter for converting into a digital code signal (D _j), the digital code signal (D _j), the digital code signal N times introduced Each time, a decimation-type low-pass filter that outputs a low-frequency signal component of the digital code signal introduced N times, an output signal (D _avg ) of the decimation-type low-pass filter, and a digital signal output by the AD converter A code signal (D _j ) is introduced to compare the magnitudes of these two digital signals, and the resulting signal is output as a high-frequency signal component. And a comparator means (15).

[0012]

The digital code signal output from the AD converter contains the instantaneous value of the low-frequency signal component and the instantaneous value of the high-frequency signal component in a superimposed form. The decimation type low-pass filter extracts only a low frequency signal component from the digital code signal. That is, every time the digital code signal is introduced N times, the low frequency component of the digital code signal introduced N times is calculated. Therefore, a signal is output by thinning to 1 / N. Note that the method of calculating the low frequency component is not limited.

The comparator means includes a low-frequency signal component output from the decimation type low-pass filter,
The magnitude of the digital code signal output from the D converter is compared. Here, the output of the low-pass filter is a low-frequency signal I _L , and the digital code signal is (low-frequency signal I _L + high-frequency signal i _H ). components i _H can be taken out.

[0014]

FIG. 1 is a diagram showing a configuration example of a receiving apparatus according to the present invention, FIG. 2 is a time chart showing signal waveforms at various parts of the apparatus of FIG. 1, and FIGS. 3 and 4 are average values of a decimation type low-pass filter. And FIG. 5 is a diagram for explaining FSK modulation.

In FIG. 1, reference numeral 1 denotes a transmission line.
The hybrid communication signal S1 as described above propagates, for example, from the process side (not shown). FIG. 2 is a diagram illustrating the operation of the hybrid communication signal and the comparator in detail. FIG. 2A shows a high-frequency signal i _H representing communication information, and the example of FIG. 2A shows an example of an FSK-modulated waveform.

The FSK modulation will be described with reference to FIG. F
The SK modulation is a modulation method in which, for example, two frequencies f ₀ and f _{1 correspond} to digital “0” and “1” as shown in FIG. That is, the signal of FIG. 5A is obtained by demodulating the FSK modulated wave of FIG. 5B, and communication information can be extracted from the time series data of 0, 1, 0,. .

[0017] Figure 2 (2) is a low-frequency signal I _L that indicates the measured value (e.g. flow rate), in the field of process control, the current signal of 4-20mA is used as previously described. The hybrid communication signal S1 is a composite waveform as shown in FIG. 2 (3) in which the waveforms of FIGS. 2 (1) and 2 (2) are superimposed.

[0018] 11 is a AD converter, samples the instantaneous value of the hybrid communication signals S1, which are sequentially and converts into a digital code signal D _j. Accordingly, when expressing the digital code signal D _j in an analog manner, the same as the hybrid communication signal S1 shown in FIG. 2 (3). As the A / D converter 11 used here, an all-parallel A / D converter, an A / D converter of an oversampling method, or the like having an operation principle of fast response is used.

Assuming that the higher frequency of the high-frequency signal i _H meaning communication information shown in FIG. 2A is f ₀ (see also FIG. 5), the sampling frequency f _AD of the AD converter 11 in the embodiment is f _AD ≧ 2 · f ₀ is selected.

Reference numeral 13 denotes a decimation type low-pass filter, which introduces a digital code signal D _j and performs, for example, an operation of D _avg = (1 / N) ΣD _j (1) (1) And this digital code signal D _j
The each of introducing N times, and outputs the average value D _avg digital code signal D _j of introducing the N times as low-frequency signal components. That is, the decimation-type low-pass filter 13 (hereinafter simply referred to as the low-pass filter 13) performs an operation of sampling N times and outputting once, that is, thinning out to 1 / N.

Σ is D_jFor j = 1 to N
Is an operation symbol indicating the addition and summation in. Also, the average value D_avg
Is calculated using another arithmetic expression other than expression (1).
Is also good. Further, as described later with reference to FIG.
Average D without any multiplication _avgYou can also ask
You. This low-pass filter 13 outputs the signal D_avgof
The output timing frequency is f_LPFThen, in the embodiment,
Is f_AD> F_LPF≧ 2 ・ f_a I have chosen. Note that the frequency f_aIs the low circumference shown in Fig. 2 (2).
Wave signal I_LIndicates the maximum frequency that has. Usually, the process
In the field of_a= About 100 Hz.

[0022] 15 is a comparator, the output signal D _avg of the low-pass filter 13, by introducing a digital code signal D _j where AD converter 11 outputs, compares the values of the two digital signals, resulting The pulse signal PD is output as a high-frequency signal component. The comparator 15 in the embodiment of FIG. 1 operates to output “1” when D _j > D _avg . FIG. 2D shows the waveform of the pulse signal PD.

It should be noted that this comparator 15 has D _j = D _avg
At this time, a comparator having a hysteresis function is usually used for the purpose of preventing the value of the comparator 15 from becoming uncertain and avoiding the influence of noise on the hybrid communication signal S1. Note that comparators with a hysteresis function are commercially available.

The operation of the receiving apparatus having the configuration shown in FIG. 1 will be described. The AD converter 11 of the receiving device includes the transmission line 1
, A hybrid communication signal S1 (analog signal) is added. AD converter 11, the hybrid communication signal S1 is sampled at a frequency f _AD, so as to output it into a digital code signal D _j. Low-pass filter 13
, For example, performs a calculation such as described above (1), and outputs the average value D _avg digital code signal D _j. here,
When performing hybrid communication, the communication information and the measurement information, so as not to interference with respect to the maximum frequency f _a of the measurement signal I _L, the frequency f ₀ of the RF signal i _H to mean a communication information,
f ₀ the relationship of f ₁ >> f _a, is set in advance in the f ₁ >> f _a.

[0025] For example, in the case of f _0> 64 · f _a, the low-pass filter 13 of the embodiment, is performed average calculation as shown in FIG. explain in detail. At time t1, it starts sampling, low-pass filter 13, the instantaneous data D1 of the digital code signal D _j, D2, D3, introducing .... And time
Assume that a total of 64 data have been introduced at time t2. Low pass filter 13, at the time of _{D avg 1 = (1/64) ·} Σ 1 D j time t2 performs calculation, and outputs the average value D _avg 1. That is, outputs thinned out digital code signal D _j to 1/64 = 1/2 ^6. Incidentally, sigma ₁ is an arithmetic symbol indicating the added sum of D _j to j = 1 to 64.

Thereafter, by performing similar operations, D _avg 2 is output at time t3, and D _avg 3 is output at time t4. As described above, the signal D is thinned out by the low-pass filter 13 to 1/64.
_{Since avg} is output, there is an advantage that subsequent electronic elements that handle the low-frequency signal D _avg can be used even if the operation speed is low. Mean values D _avg obtained by the low-pass filter 13 described above means a low-frequency signal component I _L in the hybrid communication signal S1.

When the decimation constant of the low-pass filter 13 is set to 1/2 ^N , the average value D _avg can be obtained without multiplying 1 / N in the equation (1). This will be described with reference to FIG. FIG.
3 is a diagram showing the contents of a register built in the low-pass filter 13. FIG. In this register, the sum data represented by the equation (1) is temporarily stored. In the example of FIG. 3, the addition is performed 64 times for one averaging operation. _Therefore, to obtain the average value D _avg , the contents of the register shown in FIG.
It is necessary to make 4 = 1/2 ⁶ .

Here, the binary digital data is 1/64 =
To make 1/2 ⁶ means, on the register in FIG.
It means that the data of 6 bits from the left becomes a numerical value below the decimal point. Accordingly, the data to bit data B1~MSB shifted 6 bits from the LSB as in Fig. 4 shows the average value D _avg is taken as 1/64. That is, it is only necessary to output data from B1 to MSB shown in FIG. 4 from the register holding the sum of additions without performing 1/64 multiplication.

The above will be supplementarily described by taking an average of two addition sums as an example. For example, consider a case in which the data of 101 is added twice in a binary number and an average value 101 is obtained. That is, Becomes The average value of these two times is 1
Since this means multiplication by / 2 ¹ , the data 101 shifted left by one bit is the average value.

Next, the operation in which the high frequency component i _H is obtained from the comparator 15 will be described. The comparator 15 is shown in FIG.
(3) two signals D _avg (a waveform shown by a dotted line, that is, equivalent to the low frequency signal I _L ), and D _j (a waveform shown by a solid line, that is,
The magnitude of the hybrid communication signal S1 is compared with the hysteresis E. Up to the point P1 in FIG. 2 (3), since the high frequency signal i _H is not generated (see FIG. 2 (1)), the two signals applied to the comparator 15, D _j = D _avg (2) It is. That is, the hybrid communication signal S1, the above equation (2) is satisfied since it is only the low-frequency components I _L. Further, even if a slight error occurs due to the averaging operation in the low-pass filter 13, the difference is within the width of the hysteresis E,
That is, D _j <D _avg + E (3). Therefore, the output signal PD of the comparator 15 is not inverted until the point P1 (see FIG. 2 (4)).

Then, at the point P1, a high-frequency component i _H is generated. At this point P1, the output signal of the comparator 15 is not within the range of the hysteresis E (D _j <D _avg + E).
PD does not reverse. Then, when the value of the digital code D _j further increases and reaches the point P2, D _j > D _avg + E (4), so that the output signal PD of the comparator 15 becomes “0”.
→ Invert to "1" (see FIG. 2 (4)). Thereafter, the value of the digital code D _j is directed to the reduction through a peak, becomes D _j = D _avg, even if the two data are cross, so the range of the hysteresis _{E (D j> D avg -E} ) , Comparator 15
Is not inverted. Then, when the value of the digital code D _j further decreases and reaches the point P3, D _j <D _avg −E (4), so that the output signal PD of the comparator 15 becomes “1”.
→ It is inverted to “0” (see FIG. 2 (4)).

Hereinafter, similarly, the digital code signal D _j
There is increasing, when crossing over the data D _avg low frequency from the bottom, at the time of D _j> D _avg + E, the pulse signal PD is inverted to "0" → "1". Conversely, a digital code signal D _j is decreased,
When crossing from top to bottom low frequency data D _avg is the time of D _j <D _avg -E, pulse signal PD is inverted to "1" → "0". As a result, the output signal PD of the comparator 15 is
It becomes like (4).

The waveform P of FIG. 2 (4) obtained as described above
D forms one pulse corresponding to one wave of the high frequency signal i _H (see FIGS. 2 (1) and (4)). In addition, the pulse width of the signal PD roughly corresponds to the period of the high-frequency signal i _H (see FIGS. 2A and 2B). On the other hand, this waveform PD has a low frequency signal I
Not affected by _L. Therefore, the output signal PD of the comparator 15, corresponding to the period of the high frequency signal i _H, high-l
ow is a changing signal. That is, the high-frequency signal i _H has been detected.

The output signal PD of the comparator 15 is then demodulated by a demodulator (not shown), and the communication information transmitted from the plant is reproduced. In the present application, since the demodulator has no characteristic, illustration of the demodulator is omitted. In the above description, an example has been described in which the receiving device is provided on the central control device side and the hybrid communication signal transmitted from the plant side is received on the central control device side, but the receiving device of the present invention is provided on the plant side. You may. That is, the receiving device of the present invention may be provided on the plant side, for example, on the actuator side (final operation device), and the plant may receive the hybrid communication signal transmitted from the central control device side.

[0035]

As described above, according to the present invention, a low-frequency component and a high-frequency component can be obtained from an introduced hybrid communication signal by using only one decimation-type low-pass filter having a relatively small circuit scale or arithmetic capability. Has the effect of being able to separate The decimation constant in the decimation type low-pass filter 13 is set to 1/2 ^N
, The low-pass filter 13 performs an addition operation and
Only the shift operation is required, and there is an effect that the average value D _avg can be obtained without performing the multiplication by 1 / N in the equation (1) (that is, no multiplier is required).

Since the decimation type low-pass filter 13 is used, the frequency of the signal passing through the filter 13 is reduced to 1 / N. Therefore, in subsequent signal processing, an electronic element having a low operation speed can be used, and a communication system can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a receiving apparatus according to the present invention, FIG. 2 is a time chart showing signal waveforms of respective parts of the apparatus in FIG.
And FIG. 4 are diagrams for explaining an operation of obtaining an average value by a decimation type low-pass filter, and FIG. 5 is a diagram for explaining FSK modulation.

FIG. 1 is a diagram showing a configuration example of a receiving apparatus according to the present invention.

FIG. 2 is a time chart showing signal waveforms of various parts of the apparatus of FIG. 1;

FIG. 3 is a diagram illustrating an operation of obtaining an average value by a decimation type low-pass filter.

FIG. 4 is a diagram illustrating an operation of obtaining an average value by a decimation type low-pass filter.

FIG. 5 is a diagram illustrating FSK modulation.

FIG. 6 is a diagram showing a waveform example of a hybrid communication signal.

FIG. 7 shows a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transmission line 11 AD converter 13 Decimation type low-pass filter 15 Comparator

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04J 1/00 H04L 5/06

Claims (1)

(57) [Claims] An apparatus for receiving a so-called hybrid communication signal in which a high-frequency signal is superimposed on a low-frequency signal and separating and extracting a low-frequency signal component and a high-frequency signal component. Sample the value,
An AD converter for converting it to a digital code signal (D _j), introducing the digital code signal (D _j), the digital code signal for each of introducing N times, the digital code signal introduced this N times Decimation low-pass filter that outputs low-frequency signal components, and output signal of this decimation low-pass filter
(D _avg ) and a digital code signal (D _j ) output from the AD converter are introduced to compare the magnitudes of these two digital signals, and a comparator means () for outputting the resulting signal as a high-frequency signal component 15) and a receiving device comprising: