JP7757582B2 - signal level detector - Google Patents

Description

This disclosure relates to a signal level detector for digital signals.

Signal level detectors that analogically detect the signal level of an input signal are known (see, for example, Patent Document 1 or Patent Document 2).

Devices related to the related technology are implemented using analog circuits, and specific examples of their configuration include smoothing circuits using diodes and capacitors. By detecting the envelope of the input signal, devices related to the related technology can remove high-frequency components such as noise and detect the signal level.

JP 11-298252 A JP 2000-81481

Devices related to the related technology are configured with analog circuits, which makes it difficult to flexibly switch the cutoff frequency in response to the input signal.

To solve the above problem, the present disclosure aims to provide a signal level detector that can flexibly switch the cutoff frequency depending on the input signal.

To achieve the above objective, the signal level detector disclosed herein performs smoothing digitally using a digital circuit with multiple cutoff frequencies.

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.

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.

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.

The above inventions can be combined as much as possible.

This disclosure provides a signal level detector that can flexibly switch the cutoff frequency depending on the signal level.

1 shows an example of a schematic configuration of a signal level detector according to an embodiment. 2 shows an example of a specific configuration of a signal level detector according to an embodiment. FIG. 10 is a diagram illustrating responsiveness according to an embodiment. 10A and 10B are diagrams illustrating the operation of switching the cutoff frequency according to the embodiment. 10A and 10B are diagrams illustrating the effect of switching the cutoff frequency according to the embodiment. 10A and 10B are diagrams illustrating the effect of switching the cutoff frequency according to the embodiment. 10A and 10B are diagrams illustrating the effect of switching the cutoff frequency according to the embodiment.

Embodiments of the present disclosure will be described in detail below with reference to the drawings. However, 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. In addition, components with the same reference numerals in this specification and drawings are considered to be identical to each other.

(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.

An absolute value signal refers to a signal obtained after absolute value processing has been performed on an input signal. A smoothed signal refers to a signal obtained after smoothing processing has been performed on an 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.

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

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, function block 11-1 performs absolute value processing. The signal output from function block 11-1 is an absolute value signal.

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 composed of functional blocks 12-1 to 12-9 as shown in Figure 2.

Function blocks 12-3 and 12-9 receive two signals and a control signal s_out, which will be described later. As will be described later, function blocks 12-3 and 12-9 output one of the two signals input other than the control signal s_out, depending on the value of the control signal s_out.

Function block 12-4 outputs the sum of the signal input from function block 12-3 and the signal input from function block 12-9. The signal output from function block 12-4 is the smoothed signal.

Function block 12-6 holds the smoothed signal input from function block 12-4 and outputs the value held as the previous value during the next processing at the sampling rate.

Function blocks 12-1, 12-2, 12-5, 12-7, and 12-8 multiply the input signal value by a constant displayed within the function block and output the result. Specifically, function block 12-1 multiplies the value of the absolute value signal input from function block 11-1 by (1-α), using α as the coefficient that determines the first cutoff frequency fc1, and outputs the result. Function block 12-2 multiplies the value of the absolute value signal input from function block 11-1 by (1-β), using β as the coefficient that determines the second cutoff frequency fc2, and outputs the result. Function block 12-5 multiplies the value of the smoothed signal input from function block 12-4 by a constant "ADJ" that adjusts the value to, for example, an RMS (Root Mean Square) value, and outputs the result. Note that function block 12-5 can also adjust the value of the smoothed signal input from function block 12-4 to a value other than the RMS value by changing the constant "ADJ." Function block 12-7 multiplies the previous value of the smoothed signal input from function 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. Function block 12-8 multiplies the previous value of the smoothed signal input from function 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.

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 Fig. 2. In the signal level detector 10 shown in Fig. 2, if the coefficient α is RC/(RC+Ts), the first cutoff frequency fc1 can be expressed by equation (3).
Here, Ts represents the sampling period. As shown in equation (3), the first cutoff frequency fc1 is determined by the coefficient α. Similarly, the second cutoff frequency fc2 is determined by the coefficient β. The cutoff frequency determined by the coefficient α or β is a factor that determines the responsiveness of the smoothed signal to the input signal (hereinafter, "responsiveness of the smoothed signal to the input signal" will be abbreviated as "responsiveness"). A higher cutoff frequency results in faster responsiveness, while a lower cutoff frequency results in slower responsiveness. Therefore, in this embodiment, the coefficients α and β can be said to be parameters that determine the responsiveness. In this embodiment, the coefficient β is set to be greater than the coefficient α so that the second cutoff frequency fc2 is lower than the first cutoff frequency fc1.

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

"Fast response" means that the smoothed signal quickly follows the input signal. Therefore, if the response is fast, the signal will also be able to follow fluctuations in the input signal better. Furthermore, when using a smoothed signal to detect an input signal, fast response means that the smoothed signal rises quickly, shortening the detection time.

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, resulting in hunting. Furthermore, when the response is fast, smoothing processing may not be able to completely remove noise.

On the other hand, if the response is slow, the ability to track input signal fluctuations will be poor and the detection time will be longer, but hunting will be less likely to occur and the device will be less susceptible to noise.

In order to appropriately utilize the advantages and disadvantages of these differences in responsiveness, the cutoff frequency switching unit 13 switches the cutoff frequency depending on the conditions. For example, the cutoff frequency switching unit 13 may be a state machine 13-1. State machine 13-1 receives the absolute value signal s_in1 from function block 11-1 and the smoothed signal s_in2 from function block 12-6. State machine 13-1 also outputs a control signal s_out to function blocks 12-3 and 12-9. An example of the contents of state machine 13-1 shown in Figure 2 is shown in Figure 3.

As shown in FIG. 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 a control signal s_out of 1 to the smoothing processing unit 12 to specify the first cutoff frequency fc1, which has a 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 a control signal s_out of 0 to the smoothing processing unit 12 to specify the second cutoff frequency fc2, which has a slower response.

The smoothing processing unit 12 digitally smooths the absolute value signal from the signal input unit 11 using the cutoff frequency specified by the 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, functional block 12-3 outputs the input from functional block 12-1 to functional block 12-4, and when the control signal s_out is input as 0, it outputs the input from functional block 12-2 to functional block 12-4. When the control signal s_out is input as 1, functional block 12-9 outputs the input from functional block 12-7 to functional block 12-4, and when the control signal s_out is input as 0, it outputs the input from functional block 12-8 to functional block 12-4.

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

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 having the smoothing processing unit 12 multiply the value of the smoothed signal by the aforementioned "ADJ."

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 explained using FIGS. 5(A), 5(B), 6(A), 6(B), 7(A), and 7(B). FIGS. 5(A), 6(A), and 7(A) show examples of the input signal and smoothed signal when the cutoff frequency is not switched and the cutoff frequency of the smoothing processing unit 12 is fixed at fc1. Also, FIGS. 5(B), 6(B), and 7(B) show examples of the input signal and 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.

Figures 5(A) and 5(B) show an example in which the signal level detector 10 continuously receives a high-frequency input signal with a constant amplitude from 0 seconds 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 Figure 5(A), the fast response causes the smoothed signal to fluctuate violently in response to the input signal, resulting in hunting.

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

Figures 6(A) and 6(B) show examples in which the signal level detector 10 continuously receives a high-frequency input signal containing noise. The input signals in Figures 6(A) and 6(B) are characterized by the average value after time 0.01 sec being 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 Figure 6(A), and the smoothed signal follows the input signal containing noise, resulting in residual noise in the smoothed signal.

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

Figure 7 (A) shows an example in which the signal level detector 10 receives a high-frequency input signal with a constant amplitude, with pauses during which there is no input signal at regular intervals between times 0 seconds and 0.01 seconds. Here, a pause is a time during which the input signal is 0, but the value of the input signal before the pause should be maintained. However, in a signal level detector 10 in which the cutoff frequency of the smoothing processing unit 12 is constant at fc1, as shown in Figure 7 (A), due to its fast response, it quickly follows the input signal during the pauses, causing the value of the smoothed signal to become 0.

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

Furthermore, as shown in FIG. 4, if the value of the absolute value signal s_in1 from the signal input unit 11 remains equal to or less than the value of the smoothed signal s_in2 from the smoothing processing unit 12 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. Note that the specified time tsw is set to be equal to or greater than the pause time.

In addition, in state ST3, if 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 transitions to state ST1.

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 explained using FIG. 5(C), FIG. 6(C), and FIG. 7(C). FIG. 5(C), FIG. 6(C), and FIG. 7(C) show examples of input signals and smoothed signals when smoothing processing is performed according to 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).

As shown in Figure 5(C), the signal level detector 10 of this embodiment performs smoothing processing on an input signal similar to that shown in Figure 5(B) by switching the cutoff frequency when the absolute signal value remains below the smoothed signal value for a specified period of time, 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 provides improved tracking compared to the case shown in Figure 5(B) for input signals that remain low for a period of time beyond 0.01 seconds.

As shown in Figure 6(C), the signal level detector 10 of this embodiment performs smoothing processing on an input signal similar to that shown in Figure 6(B) by switching the cutoff frequency when the absolute signal value remains below the smoothed signal value for a specified period of time, in addition to considering the magnitude relationship between the absolute signal value and the smoothed signal value. This suppresses hunting and noise in the smoothed signal, and provides improved tracking compared to the case shown in Figure 6(B) for input signals that remain low for a period of time after 0.01 seconds.

As shown in Figure 7(C), for an input signal similar to that shown in Figure 7(B), the signal level detector 10 of this embodiment performs smoothing processing by switching the cutoff frequency when the absolute signal value and the smoothed signal value remain below the smoothed signal value for a specified period of 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, maintains the smoothed signal during pauses, and provides improved tracking compared to the case shown in Figure 7(B) for input signals that remain low for a period of time after 0.01 seconds.

As described above, the signal level detector disclosed herein performs smoothing digitally using a digital circuit with multiple cutoff frequencies, thereby providing a signal level detector that can flexibly switch cutoff frequencies according to the input signal.

The signal level detector disclosed herein can be applied to the communications industry.

10: Signal level detector 11: Signal input section 12: Smoothing processing section 13: Cut-off frequency switching section

Claims (3)

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: 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;
2. The signal level detector according to claim 1, wherein 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. 3. The signal level detector according to claim 2, wherein 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 longer.