signal level detector

Abstract

To provide a signal level detector capable of flexibly switching a cut-off frequency according to an input signal.SOLUTION: A signal level detector according to present disclosure includes: a signal input part for receiving a digital input signal, performing absolute value processing in digital for the input signal, and outputting it as an absolute value signal; a smoothing processing part for smoothing the absolute value signal from the signal input part in digital and outputting it as a smoothed signal; and a cut-off frequency switching part for switching a cut-off frequency used for the smoothing by the smoothing processing part according to magnitude relationship between a value of the absolute value signal from the signal input part and a value of the smoothed signal from the smoothing processing part.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a signal level detector for digital signals. [Background technology]

[0002] BACKGROUND ART There is known a signal level detector that detects the signal level of an input signal in an analog manner (see, for example, Patent Document 1 or Patent Document 2).

[0003] The device according to the related art is realized by an analog circuit, and a specific example of the configuration is a smoothing circuit using a diode and a capacitor, etc. The device according to the related art can detect the signal level by detecting the envelope of the input signal and removing high-frequency components such as noise. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 11-298252 [Patent Document 2] Patent Publication No. 2000-81481 Summary of the Invention [Problem to be solved by the invention]

[0005] The device according to the related art is configured with analog circuits, and therefore has the problem that it is difficult to flexibly switch the cutoff frequency in accordance with the input signal.

[0006] In order to solve the above problem, an object of the present disclosure is to provide a signal level detector that can flexibly switch the cutoff frequency in accordance with the input signal. [Means for solving the problem]

[0007] To achieve the above object, the signal level detector of the present disclosure performs smoothing digitally using a digital circuit having multiple cutoff frequencies.

[0008] Specifically, the signal level detector according to the present disclosure comprises: a signal input unit that receives a digital input signal, digitally processes the input signal into an absolute value, and outputs the processed signal as an absolute value signal; a smoothing processing unit that digitally smoothes the absolute value signal from the signal input unit and outputs the smoothed signal; a cutoff frequency switching unit that switches a cutoff frequency used for the smoothing of the smoothing processing unit according to the magnitude relationship between the value of the absolute value signal from the signal input unit and the value of the smoothed signal from the smoothing processing unit; Equipped with.

[0009] The signal level detector according to the present disclosure comprises: the smoothing processing unit has a first cutoff frequency and a second cutoff frequency lower than the first cutoff frequency, the cutoff frequency switching unit outputs a control signal specifying the first cutoff frequency to the smoothing processing unit when the value of the absolute value signal from the signal input unit is greater than the value of the smoothed signal from the smoothing processing unit, and outputs a control signal specifying the second cutoff frequency to the smoothing processing unit when the value of the absolute value signal from the signal input unit is equal to or less than the value of the smoothed signal from the smoothing processing unit; The smoothing processing unit may digitally smooth the absolute value signal from the signal input unit using a cutoff frequency designated by a control signal from the cutoff frequency switching unit.

[0010] The signal level detector according to the present disclosure comprises: The cutoff frequency switching unit may output a control signal specifying the first cutoff frequency to the smoothing processing unit when a state in which the value of the absolute value signal from the signal input unit is equal to or less than the value of the smoothed signal from the smoothing processing unit continues for a specified time or longer.

[0011] The above inventions can be combined as much as possible. [Effects of the Invention]

[0012] According to the present disclosure, it is possible to provide a signal level detector that can flexibly switch the cutoff frequency according to the signal level. [Brief explanation of the drawings]

[0013] [Figure 1] 1 shows an example of a schematic configuration of a signal level detector according to an embodiment. [Figure 2] 2 shows an example of a specific configuration of a signal level detector according to an embodiment. [Figure 3] FIG. 10 is a diagram illustrating responsiveness according to an embodiment. [Figure 4] 10A and 10B are diagrams illustrating the operation of switching the cutoff frequency according to the embodiment. [Figure 5] 10A and 10B are diagrams illustrating the effect of switching the cutoff frequency according to the embodiment. [Figure 6] 10A and 10B are diagrams illustrating the effect of switching the cutoff frequency according to the embodiment. [Figure 7] 10A and 10B are diagrams illustrating the effect of switching the cutoff frequency according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These implementation examples are merely illustrative, and the present disclosure can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. Note that components with the same reference numerals in this specification and drawings indicate the same components.

[0015] (Embodiment) An example of the schematic configuration and usage of a signal level detector according to this embodiment is shown in Fig. 1. A signal level detector 10 according to this embodiment includes a signal input unit 11 that receives a digital input signal, digitally performs absolute value processing on the input signal, and outputs an absolute value signal, a smoothing processing unit 12 that digitally smooths the absolute value signal from the signal input unit 11 and outputs a smoothed signal, and a cutoff frequency switching unit 13 that switches the cutoff frequency used for smoothing in the smoothing processing unit 12 depending on the magnitude relationship between the value of the absolute value signal from the signal input unit 11 and the value of the smoothed signal from the smoothing processing unit 12.

[0016] The absolute value signal refers to a signal obtained after absolute value processing has been performed on the input signal. The smoothed signal refers to a signal obtained after smoothing processing has been performed on the absolute value signal. The signal level detector according to the present disclosure is a digital circuit, and the signal input unit 11, smoothing processing unit 12, and cutoff frequency switching unit 13 perform processing at a constant sampling rate.

[0017] An example of a specific configuration of the signal level detector according to this embodiment is shown in Fig. 2. Fig. 2 is a diagram showing the signal input unit 11, the smoothing processing unit 12, and the cutoff frequency switching unit 13 in functional blocks.

[0018] The signal input unit 11 receives an input signal and performs absolute value processing on the input signal. For example, as shown in Figure 2, a functional block 11-1 performs absolute value processing. The signal output from the functional block 11-1 is an absolute value signal.

[0019] The smoothing processing unit 12 performs smoothing processing on the absolute value signal from the signal input unit 11. For example, the smoothing processing unit 12 may be configured from functional blocks 12-1 to 12-9 as shown in FIG.

[0020] The functional blocks 12-3 and 12-9 receive two signals and a control signal s_out, which will be described later. The functional blocks 12-3 and 12-9 output one of the two signals other than the control signal s_out according to the value of the control signal s_out, as will be described later.

[0021] The functional block 12-4 outputs the signal obtained by adding the signal input from the functional block 12-3 and the signal input from the functional block 12-9. The signal output from the functional block 12-4 is a smoothed signal.

[0022] The function block 12-6 holds the smoothed signal input from the function block 12-4, and outputs the value held as the previous value at the time of the next processing at the sampling rate.

[0023] The functional blocks 12-1, 12-2, 12-5, 12-7, and 12-8 multiply the input signal value by a constant displayed in the functional block and output the result. Specifically, the functional block 12-1 multiplies the value of the absolute signal input from the functional block 11-1 by (1-α), where α is a coefficient that determines the first cutoff frequency fc1, and outputs the result. The functional block 12-2 multiplies the value of the absolute signal input from the functional block 11-1 by (1-β), where β is a coefficient that determines the second cutoff frequency fc2, and outputs the result. The functional block 12-5 multiplies the value of the smoothed signal input from the functional block 12-4 by a constant "ADJ" that adjusts the signal to, for example, an RMS (Root Mean Square) value, and outputs the result. Note that the functional block 12-5 can also adjust the value of the smoothed signal input from the functional block 12-4 to a value other than the RMS value by changing the constant "ADJ." The functional block 12-7 multiplies the previous value of the smoothed signal input from the functional block 12-6 by a coefficient α that determines the first cutoff frequency fc1 (hereinafter, "coefficient α that determines the first cutoff frequency fc1" will be abbreviated as "coefficient α") and outputs the result. The functional block 12-8 multiplies the previous value of the smoothed signal input from the functional block 12-6 by a coefficient β that determines the second cutoff frequency fc2 (hereinafter, "coefficient β that determines the second cutoff frequency fc2" will be abbreviated as "coefficient β") and outputs the result.

[0024] In the case of an RC filter, which is an analog circuit, the cutoff frequency is expressed as 1 / (2πRC). A digital circuit corresponding to this RC filter and having two cutoff frequencies is the signal level detector 10 shown in Figure 2. In the signal level detector 10 shown in Figure 2, if the coefficient α is RC / (RC+Ts), the first cutoff frequency fc1 can be expressed by equation (3).

number

[0025] Here, responsiveness will be explained using FIG. 3. FIG. 3 shows which is more advantageous, fast or slow responsiveness, from four perspectives: "detection time," "hunting," "noise resistance," and "ability to follow fluctuations in the input signal." In FIG. 3, ◯ indicates an advantage, and × indicates a disadvantage. Furthermore, hunting in this embodiment refers to drastic fluctuations in the smoothed signal.

[0026] "Fast response" means that the smoothed signal quickly follows the input signal. Therefore, if the response is fast, the smoothed signal will also be able to follow fluctuations in the input signal well. Furthermore, when the smoothed signal is used to detect the input signal, fast response means that the smoothed signal rises quickly, and therefore the detection time is shortened.

[0027] However, when the response is fast, the smoothed signal has good tracking ability with respect to fluctuations in the input signal, so when the input signal has a high frequency, the smoothed signal also becomes high frequency, causing hunting. Also, when the response is fast, smoothing processing cannot completely remove noise.

[0028] On the other hand, if the response is slow, the ability to follow fluctuations in the input signal will be poor and the detection time will be long, but hunting will be less likely to occur and the sensor will be less susceptible to the effects of noise.

[0029] Therefore, in order to appropriately utilize the advantages and disadvantages of such differences in responsiveness, the cutoff frequency switching unit 13 switches the cutoff frequency depending on the conditions. For example, a state machine 13-1 may be used for the cutoff frequency switching unit 13. The state machine 13-1 receives the absolute value signal s_in1 from the functional block 11-1 and the smoothed signal s_in2 from the functional block 12-6. The state machine 13-1 also outputs a control signal s_out to the functional blocks 12-3 and 12-9. An example of the contents of the state machine 13-1 shown in FIG. 2 is shown in FIG. 3.

[0030] 3, when the value of the absolute value signal s_in1 from the signal input unit 11 is greater than the value of the smoothed signal s_in2 from the smoothing processing unit 12, the cutoff frequency switching unit 13 may transition to state ST1 and output the control signal s_out as 1 to the smoothing processing unit 12 in order to specify a first cutoff frequency fc1 with fast response. Also, when the value of the absolute value signal s_in1 from the signal input unit 11 is equal to or less than the value of the smoothed signal s_in2 from the smoothing processing unit 12, the cutoff frequency switching unit 13 transitions to state ST2 and outputs the control signal s_out as 0 to the smoothing processing unit 12 in order to specify a second cutoff frequency fc2 with slow response.

[0031] The smoothing processing unit 12 digitally smoothes the absolute value signal from the signal input unit 11 using a cutoff frequency specified by a control signal s_out from the cutoff frequency switching unit 13. Specifically, as shown in Fig. 2, when the control signal s_out is input as 1, the functional block 12-3 outputs the input from the functional block 12-1 to the functional block 12-4, and when the control signal s_out is input as 0, the functional block 12-3 outputs the input from the functional block 12-2 to the functional block 12-4. When the control signal s_out is input as 1, the functional block 12-9 outputs the input from the functional block 12-7 to the functional block 12-4, and when the control signal s_out is input as 0, the functional block 12-9 outputs the input from the functional block 12-8 to the functional block 12-4.

[0032] With the above configuration, the smoothing processing unit 12 calculates the smoothed signal using equation (1) when the control signal s_out from the cutoff frequency switching unit 13 is 1, and calculates the smoothed signal using equation (2) when the control signal s_out from the cutoff frequency switching unit 13 is 0. Smoothed signal value = absolute signal value × (1-α) + previous value of smoothed signal × α (1) Smoothed signal value = Absolute signal value × (1-β) + Previous value of smoothed signal × β (2)

[0033] Therefore, the signal level detector 10 according to this embodiment functions as an IIR (Infinite Impulse Response) filter with a variable cutoff frequency. Furthermore, the signal level detector 10 according to this embodiment can calculate the RMS value of the input signal by the smoothing processing unit 12 multiplying the value of the smoothed signal by the aforementioned "ADJ."

[0034] The effect of the cutoff frequency switching unit 13 switching the cutoff frequency of the smoothing processing unit 12 by mutually transitioning between states ST1 and ST2 in Fig. 4 will be described using Fig. 5(A), Fig. 5(B), Fig. 6(A), Fig. 6(B), Fig. 7(A), and Fig. 7(B). Fig. 5(A), Fig. 6(A), and Fig. 7(A) show examples of an input signal and a smoothed signal when the cutoff frequency of the smoothing processing unit 12 is fixed at fc1 without switching the cutoff frequency. Fig. 5(B), Fig. 6(B), and Fig. 7(B) show examples of an input signal and a smoothed signal when the cutoff frequency switching unit 13 switching the cutoff frequency of the smoothing processing unit 12 by mutually transitioning between states ST1 and ST2 in Fig. 4.

[0035] 5A and 5B show an example in which the signal level detector 10 continuously receives a high-frequency input signal with a constant amplitude from time 0 to 0.01 seconds. In a signal level detector 10 in which the cutoff frequency of the smoothing processing unit 12 is constant at fc1, as shown in FIG. 5A, the smoothed signal fluctuates drastically in response to the input signal due to its fast response, resulting in hunting.

[0036] On the other hand, as shown in Fig. 5B, the signal level detector 10 according to this embodiment performs smoothing processing by switching the cutoff frequency through state transition between state ST1 and state ST2 in Fig. 4 depending on the magnitude relationship between the value of the absolute value signal and the value of the smoothed signal, for an input signal similar to that shown in Fig. 5A. This makes it possible to suppress hunting in the smoothed signal.

[0037] 6A and 6B show examples in which the signal level detector 10 continuously receives a high-frequency input signal containing noise. The input signals in Fig. 6A and 6B are characterized in that the average value after time 0.01 sec is lower than the average value before time 0.01 sec. In a signal level detector 10 in which the cutoff frequency of the smoothing processing unit 12 is constant at fc1, the signal level detector 10 has fast response, as shown in Fig. 6A, and the smoothed signal follows the input signal containing noise, resulting in residual noise in the smoothed signal.

[0038] On the other hand, as shown in Fig. 6(B), the signal level detector 10 according to this embodiment performs smoothing processing by switching the cutoff frequency through state transition between state ST1 and state ST2 in Fig. 4 depending on the magnitude relationship between the value of the absolute value signal and the value of the smoothed signal, for an input signal similar to that shown in Fig. 6(A). This makes it possible to suppress noise in the smoothed signal.

[0039] 7A shows an example in which the signal level detector 10 receives a high-frequency input signal with a constant amplitude, with pauses during which no input signal is present at regular intervals between 0 and 0.01 seconds. The pauses are periods during which the input signal is zero, but the value of the input signal prior to the pause should be maintained. However, in the case of a signal level detector 10 in which the cutoff frequency of the smoothing processor 12 is constant at fc1, the signal level detector 10 has a fast response, as shown in FIG. 7A, and therefore quickly follows the input signal during the pauses, resulting in the value of the smoothed signal becoming zero.

[0040] On the other hand, as shown in Fig. 7B, the signal level detector 10 according to this embodiment performs smoothing processing by switching the cutoff frequency through state transition between state ST1 and state ST2 in Fig. 4 depending on the magnitude relationship between the value of the absolute value signal and the value of the smoothed signal, for an input signal similar to that shown in Fig. 7A. This keeps the smoothed signal from becoming 0 even during pauses.

[0041] 4, when a state in which the value of the absolute value signal s_in1 from the signal input unit 11 is equal to or smaller than the value of the smoothed signal s_in2 from the smoothing processing unit 12 continues for a specified time tsw or more, the cutoff frequency switching unit 13 may transition to state ST3 and output a control signal s_out=1 specifying the first cutoff frequency fc1 to the smoothing processing unit 12. The specified time tsw is set to be equal to or larger than the pause time.

[0042] In addition, when the value of the absolute value signal s_in1 from the signal input unit 11 is greater than the value of the smoothed signal s_in2 from the smoothing processing unit 12 in the state ST3, the cutoff frequency switching unit 13 transitions to the state ST1.

[0043] The effect of the cutoff frequency switching unit 13 switching the cutoff frequency by transitioning from state ST2 to state ST3 in FIG. 4 will be described with reference to FIG. 5(C), FIG. 6(C), and FIG. 7(C). FIG. 5(C), FIG. 6(C), and FIG. 7(C) show examples of an input signal and a smoothed signal when smoothing processing is performed according to the state machine 13-1 shown in FIG. 4. The input signal in FIG. 5(C) is the same as FIG. 5(B). The input signal in FIG. 6(C) is the same as FIG. 6(B). The input signal in FIG. 7(C) is the same as FIG. 7(B).

[0044] As shown in Fig. 5C, the signal level detector 10 according to this embodiment performs smoothing processing on an input signal similar to that shown in Fig. 5B by switching the cutoff frequency when the absolute signal value is equal to or less than the smoothed signal value for a specified time or longer, in addition to considering the magnitude relationship between the absolute signal value and the smoothed signal value. This suppresses hunting in the smoothed signal, and improves the tracking ability for an input signal that continues to have a low value from 0.01 seconds onwards, compared to the case shown in Fig. 5B.

[0045] In the signal level detector 10 according to this embodiment, as shown in Fig. 6(C), for an input signal similar to that shown in Fig. 6(B), in addition to considering the magnitude relationship between the absolute signal value and the smoothed signal value, if the state in which the absolute signal value is equal to or less than the smoothed signal value continues for a specified time or longer, the cutoff frequency is switched to perform smoothing processing. This suppresses hunting and noise in the smoothed signal, and improves the tracking ability for an input signal in which low values ​​continue after 0.01 seconds compared to the case shown in Fig. 6(B).

[0046] As shown in Fig. 7C, the signal level detector 10 according to this embodiment performs smoothing processing on an input signal similar to that shown in Fig. 7B by switching the cutoff frequency when the absolute signal value is equal to or less than the smoothed signal value for a specified time or longer, in addition to considering the magnitude relationship between the absolute signal value and the smoothed signal value. This suppresses hunting of the smoothed signal, maintains the smoothed signal value during pauses, and provides improved tracking capability for an input signal that continues to have low values ​​after 0.01 seconds, compared to the case shown in Fig. 7B.

[0047] As described above, the signal level detector of the present disclosure can provide a signal level detector that can flexibly switch cutoff frequencies in accordance with the input signal by performing smoothing processing digitally using a digital circuit having multiple cutoff frequencies. [Industrial Applicability]

[0048] The signal level detector according to the present disclosure can be applied in the communications industry. [Explanation of symbols]

[0049] 10: Signal level detector 11: Signal input section 12: Smoothing processing section 13: Cutoff frequency switching section

Claims

1. a signal input unit that receives a digital input signal, digitally processes the input signal into an absolute value, and outputs the processed signal as an absolute value signal; a smoothing processing unit that digitally smoothes the absolute value signal from the signal input unit and outputs the smoothed signal; a cutoff frequency switching unit that switches a cutoff frequency used for the smoothing of the smoothing processing unit according to the magnitude relationship between the value of the absolute value signal from the signal input unit and the value of the smoothed signal from the smoothing processing unit; A signal level detector comprising:

2. the smoothing processing unit has a first cutoff frequency and a second cutoff frequency lower than the first cutoff frequency, the cutoff frequency switching unit outputs a control signal specifying the first cutoff frequency to the smoothing processing unit when the value of the absolute value signal from the signal input unit is greater than the value of the smoothed signal from the smoothing processing unit, and outputs a control signal specifying the second cutoff frequency to the smoothing processing unit when the value of the absolute value signal from the signal input unit is equal to or less than the value of the smoothed signal from the smoothing processing unit; The smoothing processing unit digitally smoothes the absolute value signal from the signal input unit using a cutoff frequency designated by a control signal from the cutoff frequency switching unit.

2. A signal level detector as claimed in claim 1.

3. The cutoff frequency switching unit outputs a control signal specifying the first cutoff frequency to the smoothing processing unit when a state in which the value of the absolute value signal from the signal input unit is equal to or less than the value of the smoothed signal from the smoothing processing unit continues for a specified time or more.

3. A signal level detector as claimed in claim 2.

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