JPH11234091A - Frequency variable filter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a frequency variable filter device which is capable of reducing power consumption. SOLUTION: A control part 4 outputs a filter selection signal selecting frequency variable filters 2 (2a, 2b, 2c and 2d) functioning by a frequency expressed through an inputted frequency signal. A bias signal which finely adjusts a tuning frequency to the frequency is generated and outputted to the selected frequency variable filter, and a bias signal by which the power consumption of the pertinent frequency variable filter becomes minimum to the frequency variable filter which is no selected. The selected frequency variable filter 2 finely adjusts the frequency, in accordance with the bias signal and the power consumption of the frequency variable filter 2 which is not selected is set to be minimum in accordance with the bias signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable frequency filter device used in a transceiver for frequency hopping communication, and more particularly to a variable frequency filter device capable of reducing power consumption.

[0002]

2. Description of the Related Art A conventional variable frequency filter device will be described with reference to FIG. FIG. 5 is a configuration block diagram of a conventional frequency variable filter device. The conventional variable frequency filter device mainly includes a first filter selector 1, a plurality of frequency variable filters 2, a second filter selector 3, and a control unit 4, as shown in FIG.
In FIG. 5, the number of frequency variable filters 2 is four.

[0006] As shown in FIG. 6, the control unit 4 includes an on / off pattern generation circuit 41 and a filter selection circuit 4.
2 and a plurality of bias generation circuits 43 provided corresponding to the frequency variable filter 2. FIG.
3 is a block diagram showing a configuration of the control unit 4.

[0004] Each component will be specifically described below. The first filter selector 1, together with the second filter selector 3, selectively outputs an RF signal (high-frequency signal) input according to a filter selection signal input from the control unit 4 to a specific frequency variable filter 2. Is what you do.

The frequency variable filter 2 has a PIN diode, and switches a tuning frequency by turning on / off the PIN diode to filter an RF signal input from the first filter selector 1 and output the RF signal to the second filter selector. This is a frequency filter for turning on / off a PIN diode according to a bias signal input from the control unit 3 described later.

Further, the variable frequency filters 2 each have, for example, a first variable frequency
280 MHz, the second frequency variable filter 2 b
80 to 325 MHz, the third frequency variable filter 2c
Are set to have different variable frequency widths (frequency bands in which the frequency variable filter 2 functions) so as to correspond to 235 to 370 MHz and the fourth frequency variable filter 2d to correspond to 370 to 400 MHz.

The second filter selector 3 selectively receives an RF signal from the variable frequency filter 2 selected by the first filter selector 1 in response to a filter selection signal input from the control unit 4. And outputs the RF signal to the outside.

The on / off pattern generation circuit 4 of the control unit 4
Reference numeral 1 denotes a circuit for generating an on / off pattern of the PIN diode of the frequency variable filter 2 in response to an input of a frequency designation signal representing a tuning frequency from the outside, and outputting the pattern to the plurality of bias generation circuits 43, respectively.

The filter selection circuit 42 of the control unit 4
Filter selection for inputting an RF signal to which frequency variable filter 2 and selecting an output of an RF signal of which frequency variable filter 2 to output to the filter selector 1 and the second filter selector 3 It outputs a signal.

The bias generation circuit 43 of the control section 4 generates a bias signal based on the on / off pattern input from the on / off pattern generation circuit 41 and outputs the bias signal to the corresponding frequency variable filter 2. Things.

Here, the bias generation circuit 43 of the control unit 4
Is specifically described with reference to FIG. FIG. 7 is a circuit diagram of the bias generation circuit 43 of the control unit 4. As shown in FIG. 7, the bias generation circuit 43 receives an on / off pattern input, converts the input / output pattern into a TTL level signal, a first transistor Q1 which operates as a forward current switch, A first resistor R1 for limiting the base current of the first transistor Q1, a second resistor R2 for stabilizing the base current of the first transistor Q1, and a third resistor for limiting the forward current Table R3
A second transistor Q2 which operates as a switch for grounding the bias signal to a reverse voltage, which is an output of the bias generation circuit 43, a fourth resistor R4 for stabilizing the base voltage of the second transistor Q2, It comprises a fifth resistor R5 for limiting the current at the time of voltage output, and a capacitor C1 for limiting the ground state of the second transistor Q2. It is assumed that the fifth resistor R5 is a resistor having a sufficiently large resistivity.

That is, when the ON / OFF pattern input via the buffer is in the Lo state (state indicating ON), the bias generation circuit 43 turns on the first transistor Q1 and turns on the second transistor Q2. When turned off, the current limited by the third resistor R3 is output, and the current is directly output to the outside.

When the on / off pattern is in the Hi state (state indicating off), the bias generation circuit 43
The first transistor Q1 is turned off, the second transistor Q2 is turned on, and the current is grounded until the capacitor C1 is saturated, so that no current is output to the outside, and the capacitor C1 is turned off. Is saturated, a current due to a reverse voltage is output to the outside via the fifth resistor R5.

Since the bias generation circuit 43 corresponds to the switching operation of one PIN diode provided in the frequency variable filter 2, if ten switching operations are required, the circuit corresponds to the number. It is provided as such.

Next, the operation of the conventional variable frequency filter device will be described. First, the control unit 4 receives an input of a frequency signal, and the on / off pattern generation circuit 41 generates an on / off pattern corresponding to the frequency represented by the frequency signal, and outputs the generated on / off pattern to the plurality of bias generation circuits 43. on the other hand,
The filter selection circuit 32 of the control unit 4 converts the filter selection signal for selecting the frequency variable filter 2 corresponding to the frequency signal into a first filter selector 1 and a second filter selector 3.
And output to

Then, the plurality of frequency variable filters 2 turn on / off the PIN diodes in accordance with the bias signals input from the corresponding bias generation circuits 43 of the control unit 4, and switch the tuning frequency.

The first filter selector 1 receives an RF signal input from the outside and selectively converts the RF signal to a frequency variable filter 2 corresponding to a filter selection signal input from the control unit 4. Output. Further, the second filter selector 3 selectively outputs the input of the RF signal from the frequency variable filter 2 according to the filter selection signal input from the control unit 4 to the outside.

Here, for example, the first filter selector 1 and the second filter selector 3 in FIG.
Assuming that the second frequency variable filter 2b is selected, the bias of the control unit 4 corresponding to the first frequency variable filter 2a, the third frequency variable filter 2c, and the fourth frequency variable filter 2d The generation circuit 43 also outputs a bias signal.

[0019]

As described above, in the above-described conventional frequency variable filter device, even the frequency variable filter not selected by the filter selection signal performs the ON / OFF operation of the PIN diode. However, there is a problem that the size becomes larger.

The present invention has been made in view of the above circumstances, and has as its object to provide a frequency variable filter device capable of reducing power consumption.

[0021]

According to a first aspect of the present invention, there is provided a frequency signal having a plurality of frequency tunable filters functioning in different frequency bands. In the variable frequency filter device that changes the tuning frequency according to the above, a control unit that operates only the variable frequency filter that functions at the frequency represented by the frequency signal is characterized in that power consumption can be reduced.

According to a second aspect of the present invention for solving the problems of the conventional example, an input high-frequency signal is filtered with a frequency represented by a separately input frequency signal as a tuning frequency, and output to the outside. In the frequency variable filter device to perform, within a specific frequency region, a plurality of frequency variable filters for fine-tuning the tuning frequency by a bias signal input from the outside are provided such that the specific frequency region is different from each other, A first filter selector for selecting a frequency variable filter to output the high-frequency signal by a filter selection signal; and a high-frequency signal output by the frequency variable filter selected by the first filter selector according to the filter selection signal. Second
And a filter selector that outputs a filter selection signal that selects a frequency variable filter that functions at the frequency from the plurality of frequency variable filters based on the frequency represented by the frequency signal, and that the selected frequency variable filter Output a bias signal for fine-tuning the tuning frequency to the frequency, and output a bias signal that minimizes the power consumption of the frequency variable filter to a frequency variable filter not selected by the filter selection signal. And power consumption can be reduced.

According to a third aspect of the present invention, there is provided a frequency variable filter device according to the second aspect, wherein the control unit includes a bias unit provided for each of the frequency variable filters. A control circuit including a generation circuit, an on / off pattern generation circuit provided corresponding to each of the bias generation circuits, and a filter selection circuit, wherein the on / off pattern generation circuit is configured such that the on / off pattern generation circuit is provided from outside. If it corresponds to a frequency variable filter that functions at the frequency represented by the input frequency signal, an on / off pattern corresponding to the frequency is generated and output, and if it does not correspond, , An on / off circuit that generates and outputs an on / off pattern that minimizes power consumption in a corresponding bias generation circuit and a corresponding frequency variable filter. A bias generation circuit that generates a bias signal from an on / off pattern input from the corresponding on / off pattern generation circuit and outputs the bias signal to a corresponding frequency variable filter; The filter selection circuit is a filter selection circuit that outputs a filter selection signal for selecting a frequency variable filter that functions at a frequency represented by the frequency signal to a first filter selector and a second filter selector. And power consumption can be reduced.

According to a fourth aspect of the present invention, there is provided a frequency variable filter device according to the second aspect, wherein the control unit includes a bias unit provided for each of the frequency variable filters. A control unit including a generation circuit, one on / off pattern generation circuit, a filter selection circuit, and a power supply control circuit, wherein the on / off pattern generation circuit is represented by a frequency signal input from outside. An on / off pattern generation circuit that generates an on / off pattern corresponding to a frequency to be output to a bias generation circuit, wherein the bias generation circuit generates an on / off pattern from an on / off pattern input from the on / off pattern generation circuit. A bias generation circuit that generates a bias signal and outputs the bias signal to a corresponding frequency variable filter; The filter selection signal for selecting a frequency variable filter for the first filter selector, second
And a filter selection circuit for outputting to the filter selector, wherein the power supply control circuit supplies power only to the bias generation circuit corresponding to the frequency variable filter functioning at the frequency, and corresponds to the frequency variable filter functioning at the frequency. It is characterized by a power supply control circuit that does not supply power to a bias generation circuit that does not perform power generation, and power consumption can be reduced.

According to a fifth aspect of the present invention, there is provided a frequency variable filter device according to the second aspect, wherein the control unit includes a bias unit provided for each of the frequency variable filters. A control unit including a generation circuit, an on / off pattern generation circuit, and a filter selection circuit, wherein the on / off pattern generation circuit corresponds to a frequency represented by a frequency signal input from outside. An on / off pattern generation circuit that generates an on / off pattern and outputs the generated on / off pattern to the bias generation circuit, wherein the bias generation circuit is configured to receive a bias signal from the filter selection circuit while generating an instruction signal. Generating a bias signal from an on / off pattern input from the on / off pattern generation circuit and outputting the bias signal to a corresponding frequency variable filter A bias generation circuit that outputs a bias signal that minimizes power consumption in the corresponding frequency variable filter to the corresponding frequency variable filter when the instruction signal is not input, and the filter selection circuit is configured to output the bias signal at the frequency. A filter selection signal for selecting a functioning variable frequency filter is output to a first filter selector and a second filter selector, and
A filter selection circuit that outputs the instruction signal to a bias generation circuit corresponding to a frequency variable filter selected by the filter selection signal,
Power consumption can be reduced.

[0026]

Embodiments of the present invention will be described with reference to the drawings. The variable frequency filter device (the present device) according to the present invention is capable of reducing the power consumption by stopping the control of the frequency variable filter that is not selected.

This device is similar to the conventional frequency variable filter device shown in FIG. 5, but the operation of the control unit 4 is slightly different. As shown in FIG. 1, the control unit 4 of the present apparatus includes an on / off pattern generation circuit 41 ', a filter selection circuit 42, and a bias generation circuit 43. FIG. 1 is a configuration block diagram of the control unit 4 of the present apparatus. Here, the filter selection circuit 42 and the bias generation circuit 43 are the same as those in the related art, and thus the description is omitted.

The on / off pattern generation circuit 41 'is provided corresponding to the bias generation circuit 43.
Further, the on / off pattern generation circuit 41 'receives the input of the frequency signal, and if the frequency signal is a frequency band in which the corresponding frequency variable filter 2 functions, the on / off pattern generation circuit 41' performs the same as in the conventional case. Is generated and output.

Further, an on / off pattern generation circuit 4
Reference numeral 1 'is for reducing the power consumption of the on / off pattern data when the frequency signal is not in the frequency band in which the corresponding frequency variable filter 2 functions when the frequency signal is input. On / off pattern data with low power consumption is considered to be in an all-off state in the case of the bias generation circuit specifically shown in FIG.

According to the present apparatus having such a control unit 4, the bias generation circuit 43 of the control unit 4 corresponding to the frequency variable filter 2 that does not function with respect to the frequency signal input to the control unit 4 generates the bias signal. Is not generated, the on / off operation of the PIN diode in the variable frequency filter 2 is stopped, and the power consumption in the control unit 4 and the variable frequency filter 2 can be reduced.

As shown in FIG. 2, the control unit 4 of the present apparatus includes an on / off pattern generation circuit 41 similar to the conventional one.
In addition to the filter selection circuit 42 and the bias generation circuit 43, power is supplied only to the bias generation circuit 43 corresponding to the frequency variable filter 2 functioning for the input frequency signal, and the other bias generation circuits 43 And a power supply control circuit 44 for not supplying power to the power supply. FIG. 2 shows the control unit 4 of the apparatus.
It is another block diagram of a structure.

According to the present apparatus, no power is supplied to the bias generation circuit 43 of the control unit 4 corresponding to the frequency variable filter 2 which does not function with respect to the input frequency signal. There is an effect that the on / off operation of the PIN diode in the frequency variable filter 2 is stopped, and the power consumption in the control unit 4 and the frequency variable filter 2 can be reduced.

Further, as shown in FIG. 3, the control unit 4 of the present apparatus includes a bias generation circuit 41, a filter selection circuit 42 ', and a bias generation circuit provided corresponding to the frequency variable filter 2. And a circuit 43 '. FIG. 3 is a block diagram showing another configuration of the control unit 4 of the present apparatus. Here, the on / off pattern generation circuit 4
1 is the same as the conventional one, and the description is omitted.

The filter selection circuit 42 'receives the input of the frequency signal, outputs a filter selection signal as in the prior art, and generates a bias corresponding to the frequency variable filter 2 functioning at the frequency represented by the frequency signal. Circuit 4
Signal for instructing generation of bias signal at 3 '(instruction signal)
And the other bias generation circuit 4
No instruction signal is output to 3 '.

The bias generation circuit 43 'receives an instruction signal from the filter selection circuit 42'
As in the conventional case, a bias signal is generated according to the on / off pattern signal input from the on / off pattern generation circuit 41 and output to the corresponding frequency variable filter 2.

When no instruction signal is input from the filter selection circuit 42 ', the bias generation circuit 43' enters a state where power consumption is reduced, and the corresponding frequency variable filter minimizes power consumption. The bias signal is output as follows.

Specifically, the bias generation circuit 43 '
It can be considered as shown in FIG. FIG.
Is a circuit diagram illustrating an example of a bias generation circuit 43 ′. The bias generation circuit 43 'shown in FIG. 4 is almost the same as the conventional bias generation circuit 43, except that the buffer has an on / off pattern input and the filter selection circuit 4
This is different from the conventional one in that a three-state buffer receiving the input of the instruction signal from 2 'is replaced by a pull-up resistor R6 connected to its output.

That is, the bias generation circuit 4 shown in FIG.
The three-state buffer 3 'includes a filter selection circuit 4
If there is no input of the instruction signal from 2 ', the output will be in a high impedance state. Therefore, the bias generation circuit 43 '
Is turned off by the action of the pull-up resistor R6.

The bias generation circuit 4 shown in FIG.
The three-state buffer 3 'includes a filter selection circuit 4
When a signal is input from 2 ', the operation is the same as that of the buffer shown in FIG.

According to this apparatus, the bias generation circuit 43 of the control unit 4 corresponding to the frequency variable filter 2 that does not function with respect to the frequency signal input to the control unit 4 does not generate a bias signal. Thus, there is an effect that the operation of turning on / off the PIN diode in the frequency variable filter 2 is stopped, and the power consumption in the control unit 4 and the frequency variable filter 2 can be reduced.

[0041]

According to the first aspect of the present invention, only a frequency variable filter that functions at a frequency represented by a frequency signal input from the outside among a plurality of frequency variable filters that function in different frequency bands is operated. Since the variable frequency filter device having the control unit is used, there is an effect that power consumption can be reduced without operating a non-functional variable frequency filter.

According to the second aspect of the present invention, based on the frequency represented by the frequency signal inputted from the outside, the control unit outputs a filter selection signal for selecting a frequency variable filter functioning at the frequency. A bias signal for fine-tuning the tuning frequency to the frequency is output to the selected frequency variable filter, and a bias signal that minimizes the power consumption of the frequency variable filter is output to the non-selected frequency variable filters. The first filter selector outputs a high-frequency signal input from the outside to a frequency variable filter selected by the filter selection signal,
Since the second filter selector is a frequency variable filter device that selects and outputs a high-frequency signal output from the frequency variable filter selected by the first filter selector, the frequency variable that does not function at the frequency specified by the frequency signal This has the effect of minimizing power consumption in the filter and reducing power consumption.

According to the third aspect of the present invention, the control unit includes:
When it corresponds to a frequency variable filter that is provided corresponding to each of the bias generation circuits and functions at a frequency represented by an externally input frequency signal, an on / off pattern corresponding to the frequency is generated. Otherwise, an ON / OFF pattern generation circuit that generates and outputs an ON / OFF pattern that minimizes power consumption in the corresponding bias generation circuit and frequency variable filter, and an input from the ON / OFF pattern generation circuit And a filter selection circuit that outputs a filter selection signal that selects a frequency variable filter that functions at the frequency represented by the frequency signal. 3. The variable frequency filter device according to claim 2, wherein the control unit comprises: Because there, the variable frequency filter which does not function at the frequency specified by the frequency signal, and to minimize power consumption in the bias generating circuit corresponding thereto,
This has the effect of reducing power consumption.

According to the fourth aspect of the present invention, the control unit includes:
An on / off pattern generation circuit that generates an on / off pattern corresponding to the frequency represented by the frequency signal input from the outside and outputs the generated on / off pattern to the bias generation circuit; and a frequency that functions at the frequency represented by the frequency signal. A power supply control circuit that supplies power only to a bias generation circuit corresponding to the variable filter and does not supply power to the other bias generation circuits, and a bias that receives an on / off pattern and generates a bias signal The frequency variable filter device according to claim 2, wherein the control unit includes a generation circuit and a filter selection circuit that outputs a filter selection signal that selects a frequency variable filter that functions at a frequency represented by the frequency signal. Outputs a bias signal for fine frequency adjustment to a frequency variable filter that does not function at the frequency specified by the signal. By lest in, and the frequency variable filter, so as not to operate the bias generating circuit corresponding thereto, there is an effect that power consumption can be reduced.

According to the fifth aspect of the present invention, the control unit includes:
An on / off pattern generation circuit that generates an on / off pattern corresponding to a frequency represented by an externally input frequency signal and outputs the generated on / off pattern to a bias generation circuit; A bias generation circuit that generates a bias signal according to an input on / off pattern and outputs a bias signal that minimizes power consumption in the frequency variable filter when no instruction signal is input; A filter that outputs a filter selection signal that selects a frequency variable filter that functions at the frequency to be output, outputs an instruction signal to a bias generation circuit corresponding to the frequency variable filter, and does not output an instruction signal to other bias generation circuits. 3. A control unit having a selection circuit.
Since the above-described frequency variable filter device is used, there is an effect that power consumption can be reduced by minimizing the power consumption of the frequency variable filter that does not function at the frequency designated by the frequency signal and the corresponding bias generation circuit.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram of a control unit 4 of the present apparatus.

FIG. 2 is another configuration block diagram of a control unit 4 of the present apparatus.

FIG. 3 is another configuration block diagram of a control unit 4 of the present apparatus.

FIG. 4 is a circuit diagram illustrating an example of a bias generation circuit 43 ′.

FIG. 5 is a configuration block diagram of a conventional frequency variable filter device.

FIG. 6 is a configuration block diagram of a control unit 4.

FIG. 7 is a circuit diagram of a bias generation circuit 43 of the control unit 4.

[Explanation of symbols]

1 ... first filter selector, 2 ... frequency variable filter, 3 ... second filter selector, 4 ... control unit,
41, 41 '... ON / OFF pattern generation circuit, 42, 4
2 ': filter selection circuit; 43, 43': bias generation circuit; 44: power supply control circuit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuji Takahashi 3-14-20 Higashinakano, Nakano-ku, Tokyo Inside Kokusai Electric Corporation

Claims (5)

[Claims] 1. A frequency variable filter device comprising a plurality of frequency variable filters functioning in different frequency bands and changing a tuning frequency in accordance with a frequency signal input from the outside, functions at a frequency represented by the frequency signal. A frequency variable filter device comprising a control unit that operates only a frequency variable filter. 2. A frequency variable filter device for filtering an input high-frequency signal using a frequency represented by a separately input frequency signal as a tuning frequency and outputting the same to the outside. A plurality of frequency variable filters for fine-tuning the tuning frequency by a bias signal to be provided are provided so that the specific frequency regions are different from each other, and a frequency variable filter to output the high frequency signal is selected by a filter selection signal. A first filter selector that outputs a high-frequency signal output by the frequency variable filter selected by the first filter selector based on the filter selection signal; and a second filter selector that outputs a high-frequency signal based on the frequency represented by the frequency signal. From the plurality of frequency variable filters, A filter selection signal for selecting a number variable filter is output, and a bias signal for finely adjusting a tuning frequency to the frequency is output to the selected frequency variable filter, and a frequency variable filter not selected by the filter selection signal is output to the selected frequency variable filter. And a control unit that outputs a bias signal that minimizes power consumption of the frequency variable filter. 3. A control section comprising: a bias generation circuit provided for each of the frequency variable filters; an on / off pattern generation circuit provided for each of the bias generation circuits; and a filter selection circuit. The on / off pattern generation circuit, when the self-operation pattern generation circuit corresponds to a frequency variable filter that functions at a frequency represented by a frequency signal input from the outside, Is generated and output, and if not, an on / off pattern that minimizes the power consumption of the corresponding bias generation circuit and the corresponding frequency variable filter is generated. An on / off pattern generation circuit that outputs the data from the on / off pattern generation circuit. And a bias generation circuit that generates a bias signal from a / off pattern and outputs the bias signal to a corresponding frequency variable filter, wherein the filter selection circuit selects a frequency variable filter that functions at a frequency represented by the frequency signal. 3. The variable frequency filter device according to claim 2, wherein the filter selection circuit outputs a signal to the first filter selector and the second filter selector. 4. The control unit includes a bias generation circuit provided for each of the frequency variable filters, one on / off pattern generation circuit, a filter selection circuit, and a power supply control circuit. The on / off pattern generation circuit is an on / off pattern generation circuit that generates an on / off pattern corresponding to a frequency represented by an externally input frequency signal and outputs the generated on / off pattern to a bias generation circuit. The bias generation circuit is a bias generation circuit that generates a bias signal from an on / off pattern input from the on / off pattern generation circuit and outputs the bias signal to a corresponding frequency variable filter. A first filter selector and a second filter selector for selecting a frequency variable filter that functions in The power supply control circuit supplies power only to a bias generation circuit corresponding to a frequency variable filter that functions at the frequency, and generates a bias that does not correspond to a frequency variable filter that functions at the frequency. 3. The variable frequency filter device according to claim 2, wherein the variable frequency filter device is a power supply control circuit that does not supply power to the circuit. 5. A control unit comprising: a bias generation circuit provided corresponding to each of the frequency variable filters; one on / off pattern generation circuit; and a filter selection circuit. The / off pattern generation circuit is an on / off pattern generation circuit that generates an on / off pattern corresponding to a frequency represented by a frequency signal input from the outside and outputs the generated on / off pattern to the bias generation circuit. Generating a bias signal from an on / off pattern input from the on / off pattern generation circuit and outputting a corresponding frequency variable filter while an instruction signal for instructing generation of a bias is input from the filter selection circuit; And when no instruction signal is input, the power consumption of the corresponding frequency variable filter is minimized. A bias generation circuit that outputs a bias signal to a corresponding frequency variable filter, wherein the filter selection circuit outputs a filter selection signal that selects a frequency variable filter functioning at the frequency to a first filter selector and a second filter selector 3. The frequency variable filter device according to claim 2, wherein the filter selection circuit outputs the instruction signal to a bias generation circuit corresponding to the frequency variable filter selected by the filter selection signal.