TWI389479B - Communication architecture achieving full-duplex transmission using one transmission media and method thereof - Google Patents

Description

Communication architecture and method for achieving full duplex transmission by single transmission medium

The present invention relates to an electronic signal transmission architecture, in particular to a multi-computer switch (KVM) system, which is electrically connected to a plurality of computers and a set of human interface devices, and includes a transmission medium, and a single transmission medium uses frequency division multiplexing (FDD). The data transmission mode can be applied to the above architecture or the system.

The traditional Category 5 (Cat5) cable KVM system, due to wire restrictions (which have four pairs of twisted-pair cables: twisted-pair cable), can only be used with one pair of stranded wires as a communication transmission medium. Therefore, in order to achieve the purpose of two-way communication, it is necessary to transmit data in different directions at different times, which is called a half-duplex or a time division duplex (TDD) transmission system. For example, the first diagram (a) is a circuit diagram of a conventional half-duplex single transmission medium. The conventional half-duplex single transmission medium 1 includes a transmitter 11 on the left side, a receiver 12 and a terminating resistor Rhd1, a twisted pair cable 15 having a first cable and a second cable, and It is located at one of the transmitters 13, a receiver 14, and a terminating resistor Rhd2 on the right side. The transmitter 11 and the receiver 12 respectively have a first input terminal (DI/B), a second input terminal (DE/A), a first output terminal (B/RO) and a second output terminal ( A/RE), the terminating resistor Rhd1, the transmitter 11 and the receiver 12 are coupled to the first and second cable lines at points B and A, respectively. The transmitter 13 and the receiver 14 respectively have a first input terminal (DE/B), a second input terminal (DI/A), a first output terminal (B/RO) and a second output terminal ( A/RE), the terminating resistor Rhd2, the transmitter 13 and the receiver 14 are also coupled to the first and second cable lines respectively to B and A Wait for two points. The first figure (b) is an equivalent circuit diagram of the first figure (a), wherein the transmitter 11 is simplified to have an input terminal TX and an output terminal coupled to the twisted pair cable 15, the receiver 12 being simplified To have an input coupled to the twisted pair cable 15 and an output RX, and the transmitter 13 is also simplified to have an input TX, and an output coupled to the twisted pair cable 15 for receiving The device 14 is simplified to have an input coupled to the twisted pair cable 15 and an output RX.

The Full-Duplex transmission system ensures that the uplink/downlink (TX/RX) signals can have their own transmission bandwidth, and the simplest implementation of a full-duplex transmission system for the uplink and downlink signals by different transmission media For Bi-directional transmission. For example, the second diagram (a) is a circuit diagram of a conventional full-duplex independent transmission medium, which includes a first transmission medium, including a transmitter 21 on the left side and a termination resistor Rfd1, and a first cable. a first twisted pair cable 25 of a line and a second cable, and a receiver 23 and a terminating resistor Rfd2 on the right side, and a second transmission medium, including a receiver 22 on the left side and a terminating resistor Rfd3 A second twisted pair cable 26 having a first cable and a second cable, and a transmitter 24 and a terminating resistor Rfd4 on the right side. The receiver 22 and the transmitter 24 respectively have a first input terminal (DE/B), a second input terminal (DI/A), a first output terminal (Z/RE) and a second output terminal ( Y/RO), the transmitter 21 and the receiver 23 are respectively coupled to the first and second cable lines of the first twisted pair cable 25 at four points A and B and Y and Z. The terminating resistor Rfd1 and the first and second cable wires of the first twisted pair cable 25 are coupled to two points, A and B. The terminating resistor Rfd2 is respectively the first of the first twisted pair cable 25 The second cable is coupled to two points, Y and Z. The receiver 22 and the transmitter 24 respectively have a first input terminal (Z/RE), a second input terminal (Y/RO), a first output terminal (DE/B) and a second output terminal ( DI/A), the receiver 22 and the transmitter 24 are coupled to the first and second cable lines of the second twisted pair cable 26 at four points of Z and Y, and B and A, respectively. The terminating resistor Rfd3 is coupled to the first and second cable wires of the second twisted pair cable 26 at two points, Z and Y, respectively. The terminating resistor Rfd4 is coupled to the first and second cable lines of the second twisted pair cable 26 at two points, B and A, respectively.

The second diagram (b) is an equivalent circuit diagram of the second diagram (a), wherein the transmitter 21 is simplified to have an input terminal TX and an output terminal coupled to the first twisted pair cable 25, the receiver 23 is simplified to have an input coupled to the first twisted pair cable 25 and an output RX, and the transmitter 24 is also simplified to have an input TX, and an output coupled to the second twisted pair The cable 26 is simplified with an input coupled to the second twisted pair cable 26 and an output RX.

However, the Cat5 KVM system is still limited by the number of wires and cannot be implemented using this full-duplex transmission architecture.

Since the traditional half-duplex transmission system must introduce a guard time (Time) on the time domain as a flag for the uplink/downlink (TX/RX) signal, it is waiting for the time to return the data. Equivalent to the waste of transmission bandwidth.

The third figure (a) is a waveform diagram of the transmission intensity corresponding transmission band (w) of a conventional half-duplex transmission system. Since the traditional half-duplex transmission system transmits or receives signals in different time periods, its transmission and reception frequencies can be in the same frequency band, as shown in the third figure (a). Shown.

The third figure (b) is a waveform diagram of the transmission amplitude corresponding to the transmission time (t) of a conventional half-duplex single transmission system. Since the traditional half-duplex single transmission system must transmit or receive signals in different time periods, its transmission and reception periods are different, but the protection time as described above must be introduced as the uplink/downlink (TX/RX). The flag of the signal is shown in Figure (b) of the third figure.

The fourth figure (a) is a waveform diagram of the transmission intensity corresponding transmission band (w) of a conventional full-duplex independent transmission system. Since the traditional full-duplex transmission system can simultaneously transmit and receive signals in the same time period, its transmission and reception frequencies must be in different frequency bands, and a guard band (Guard Band) must be introduced to separate the transmission and reception frequencies, such as Figure 4 (a) shows.

The fourth figure (b) is a waveform diagram of the transmission amplitude corresponding transmission time (t) of a conventional full-duplex independent transmission system. Since the conventional full-duplex transmission system can simultaneously transmit and receive signals in the same time period, the transmission and reception periods are the same as shown in the fourth figure (b).

As a result of the job, the inventor, in view of the lack of prior art, is thinking about the idea of improving the invention, and finally invented the communication architecture and method for achieving full-duplex transmission with a single transmission medium.

One of the objectives of the present invention is to provide a single transmission medium to achieve a communication architecture of a full-duplex transmission system for solving the uplink/downlink transmission of the Cat5 KVM system in a conventional half-duplex system, the bandwidth of which is limited by the protection time, and the single transmission medium It is also possible to avoid the need for additional independent transmission media as in traditional full-duplex independent transmission systems. Disadvantages.

Another purpose of this case is to use frequency division multiplexing to make the signals of different frequency bands in the uplink and downlink, using the orthogonality of different frequencies in the vector space, so that they can be mutually interfered in the same transmission medium. Delivery in different directions. Among them, transmission channels of different frequencies must have guard bands of a certain frequency band to ensure good isolation of different frequency bands.

Another object of the present invention is to provide an electronic signal transmission architecture. The electronic signal transmission architecture includes a transmission medium having a first end and a second end. A high speed signal and a low speed signal are simultaneously on the transmission medium. Transmitting, a first communication module, a first high-pass filter coupled to the first end and the first communication module, for transmitting or receiving the high-speed signal, a first low-pass filter, coupled Connected to the first end and the first communication module, for transmitting or receiving the low speed signal, a second communication module, and a second high pass filter coupled to the second end and the second communication The module is configured to transmit or receive the high speed signal, and a second low pass filter coupled to the second end and the second communication module for transmitting or receiving the low speed signal.

According to the above concept, the high speed signal and the low speed signal are transmitted in a frequency division multiplexing (FDD) manner.

According to the above concept, the first and the second low pass filters each have a low pass band, and the frequency of the low speed signal is in the low pass band range, the first and the second high pass The filters each have a high pass band, and the frequency of the high speed signal is in the high pass band range.

According to the above concept, the first and the second high pass filter and the first A guard band between one and the second low pass filter is greater than 500 kHz.

According to the above concept, the ratio of the high speed signal to the low speed signal frequency is greater than four.

According to the above concept, each of the first and second high pass filters is selected from any one of a Chebyshev high pass filter, a Butterworth high pass filter and a Bessel high pass filter, and each of the first and second The low pass filter is selected from a Chebyshev low pass filter, a Butterworth low pass filter and a Bessel low pass filter.

According to the above concept, the transmission medium is one of four pairs of twisted pairs of a Category 5 (Cat5) cable.

According to the above concept, when the architecture is in a first state, the first communication module is configured to receive the high speed signal and transmit the low speed signal, and the second communication module is configured to receive the low speed signal and transmit The high speed signal, and when the architecture is switched to a second state, the second communication module is configured to receive the high speed signal and transmit the low speed signal, and the first communication module is configured to receive the low speed signal and The high speed signal is transmitted.

According to the above concept, the switching between the first state and the second state is controlled via a software.

According to the above concept, the switching between the first state and the second state is controlled via a switching device and at least one switch.

According to the above concept, each of the first and second communication modules further includes a transmitter and a receiver, wherein when the transmitter transmits the high speed signal, the receiver receives the low speed signal when the sending Issue the low At the speed signal, the receiver receives the high speed signal.

The purpose of the present invention is to provide a KVM system, which is electrically connected to a plurality of computers and a set of human interface devices, and includes a switching device for switching signal transmission between the group of human interface devices and the computers. The path, a transmission medium, has a first end and a second end, a high speed signal and a low speed signal are simultaneously transmitted on the transmission medium, a first communication module, a first high pass filter, and a coupling Connected to the first end and the first communication module, for transmitting or receiving the high-speed signal, a first low-pass filter coupled to the first end and the first communication module for transmitting Receiving or receiving the low-speed signal, a second communication module, and a second high-pass filter coupled to the second end and the second communication module, for transmitting or receiving the high-speed signal, and a second The low pass filter is coupled to the second end and the second communication module for transmitting or receiving the low speed signal.

A further object of the present invention is to provide a control method for a four-to-many computer switch (KVM) system for a full-duplex transmission architecture, comprising the following steps: (a) providing a first end and a first a single transmission medium, a high speed signal and a low speed signal; and (b) transmitting the high speed and the low speed signal by using a frequency division multiplexing (FDD) method, so that the high speed and the low speed signal can be simultaneously in the single The first end of the transmission medium is forwarded to the second end.

According to the above concept, the method further includes the following steps: (c) providing a first high pass filter coupled to the first end and a first low pass filter, and coupling to one of the second ends a second high pass filter and a second low pass filter; and (d) passing the first and the second high pass filter There is a guard band between the pass band and one of the stop bands of the first and second low pass filters, wherein the guard band is the difference between the pass band and the stop band.

The above described objects, features, and advantages of the present invention will become more apparent and understood.

Please refer to FIG. 5, which is a schematic diagram showing the architecture of an electronic signal transmission architecture in accordance with a preferred embodiment of the present invention. The electronic signal transmission architecture 3 includes a transmission medium 35 having a first end and a second end, wherein a high speed signal and a low speed signal are simultaneously in the transmission medium (for example, a pair of twisted pairs of a Cat5 cable) The first pair of high-pass filters 31 are coupled between the first end of the transmission medium 35 and the first communication module 36 for transmitting or receiving high-speed signals, first The low-pass filter 32 is coupled between the first end of the transmission medium 35 and the first communication module 36 for transmitting or receiving a low-speed signal, and a second high-pass filter 33 coupled to the transmission medium 35. The second end is connected to the second communication module 37 for transmitting or receiving the high speed signal, and a second low pass filter 34 is coupled to the second end of the transmission medium 35 and the second communication module 37. Between, used to transmit or receive the low speed signal.

Please refer to the sixth figure, which shows a first subsystem 311 and a first low-pass filter 32 of the first high-pass filter 31 of an electronic signal transmission architecture according to a preferred embodiment of the present invention. A circuit diagram of a first preferred embodiment of a subsystem 321. The first subsystem 311 includes capacitors C1, C2 and C3 and inductors L1 and L2, and the first subsystem 321 includes a capacitor C4. With C5 and inductors L3, L4 and L5. Each of the first preferred embodiments in the sixth figure above is a set of Chebyshev high-pass filters whose pass band is 1 MHz and a set of Cehbyshev low-pass filters whose stop band is A pair of four pairs of twisted pairs of Cat5 cables that are achieved at 250 KHz, thereby providing two sets of transmission channels of different frequencies, wherein the guard band is 750 KHz. Therefore, the bit rate of the high-speed transmission (TX) signal cannot be lower than 2 Mbps, and the bit rate of the low-speed reception (RX) signal cannot be higher than 500 Kbps. The high speed signal input 埠 is defined as P1, the low speed signal input 埠 is defined as P2, and the output of the connected Cat5 cable is defined as P3. Of course, the mode of the filter can be selected arbitrarily. In addition to the Chebyshev filter used above, a Butterworth filter or a Bessel filter can also be selected.

We can use the time domain simulation that is closest to the real operating environment to test the packet transmission correctness of the full duplex transmission system proposed in accordance with the preferred embodiment of the present invention. The seventh diagram (a) is a circuit diagram of the analog line when tested using PSPICE. The circuit diagram of the analog circuit includes, for example, a circuit diagram of the second preferred embodiment of the first subsystem 311 of the first high-pass filter 31, including capacitors C5, C6 and C7 and inductors L1 and L2, a second The circuit diagram of the preferred embodiment of subsystem 312 includes capacitors C8, C9 and C10 and inductors L3 and L4, and a circuit diagram of a second preferred embodiment of the first subsystem 321 of the first low pass filter 32 includes Capacitors C12 and C24 and inductors L7, L8 and L17. In addition, the second high-pass filter 33 also includes a first subsystem 331 and a second subsystem 332, and the second low-pass filter 34 also includes a first subsystem 341 and a second subsystem 342, and displays A circuit diagram of a preferred embodiment of the first communication module 36 and the second communication module 37. Because the symbols of the electronic components in the seventh figure (a) have been marked on the In the circuit diagram, those skilled in the art can understand what kind of electronic components they represent. For example, U59 is an IC chip, so no more complaints will be made here. From the high-speed channel or the low-speed channel in the seventh diagram (a), after the high- and low-speed signals are transmitted in both directions at the same time, the corresponding high-speed or low-speed signals are parsed at the associated high-speed or low-speed receiving end.

Figure 7 (b) is an equivalent circuit diagram of the seventh diagram (a), wherein the twisted pair cable 35 further includes a first cable 351 and a second cable 352, and the first and second communication modes Groups 36/37 further include a transmitter 361/371 and a receiver 362/372; wherein when the transmitter 361/371 transmits the high speed signal, the receiver 362/372 receives the low speed signal when When the transmitter 361/371 issues the low speed signal, the receiver 362/372 receives the high speed signal. When the architecture 3 is in a first state, the first communication module 36 is configured to receive the high speed signal and transmit the low speed signal, and the second communication module 37 is configured to receive the low speed signal and transmit the high speed. The second communication module 37 is configured to receive the high-speed signal and transmit the low-speed signal, and the first communication module 36 is configured to receive the low-speed signal and transmit when the architecture is switched to a second state. The high speed signal is output, wherein the switching between the first state and the second state is controlled via a switching device 363/373 and at least one switch, such as 364 and 365 and 374 and 375. The switching between the first state and the second state is controlled via a software.

In addition, the full-duplex transmission system 3 according to the preferred embodiment of the present invention can be tested according to the S-Parameter simulation, and the relevant waveform diagram of the simulation result is as shown in the eighth figure. In the eighth figure, it can be observed that the low speed channel is at 250KHz (bit rate is 500Kbps), and the Insertion Loss S32 still has excellent performance at 250KHz. The flatness (Flatness), and Return Loss S22 is also quite low, only 24.17dB, so that the low-speed signal has low distortion within 250KHz of the stop band. When the frequency is higher than 250 kHz, the S32 is at a high roll-off speed. Similarly, when the high-speed channel is at 1MHz (bit rate is 500Kbps), the Insertion Loss S31 has good flatness at 1MHz, and the Return Loss S11 is also quite low, only 20.21dB. When the frequency is 560KHz, this is the Cross-over Frequency. At this time, Insertion Loss S32=S31=26.9dB, indicating that the high and low speed channels have good isolation.

Of course, the electronic signal transmission architecture 3 (see, for example, the fifth diagram) of the preferred embodiment of the present invention can also be applied to a multi-computer switch (KVM) system, electrically connecting a plurality of computers and a group of humanities. The interface device includes a switching device that switches a signal transmission path between the group of human interface devices and the computers, and the electronic signal transmission architecture 3.

In summary, the present invention provides a single transmission medium to achieve a communication architecture of a full-duplex transmission system, which is used to solve the problem that the bandwidth of the Cat5 KVM system is limited to the protection time on the traditional half-duplex system. The single transmission medium can also avoid the disadvantage that the traditional full-duplex independent transmission system must additionally use an independent transmission medium, so it has excellent industrial utilization.

Therefore, even though the present invention has been described in detail by the above-described embodiments, it can be modified by those skilled in the art, and is not intended to be protected as claimed.

1‧‧‧Electronic signal transmission architecture with half-duplex single transmission medium

11,13,21,24,361,371‧‧‧transmitters

12,14,22,23,362,372‧‧‧ Receiver

15,35‧‧‧Twisted pair cable

25‧‧‧First twisted pair cable

26‧‧‧Second twisted pair cable

2‧‧‧Electronic signal transmission architecture with full-duplex independent transmission medium

3‧‧‧Electronic signal transmission architecture with full duplex single transmission medium

31‧‧‧First high-pass filter

32‧‧‧First low pass filter

311,321,331,341‧‧‧ first subsystem

312,322,332,342‧‧‧second subsystem

33‧‧‧Second high-pass filter

34‧‧‧Second low pass filter

351‧‧‧First cable

352‧‧‧Second cable

36‧‧‧First Communication Module

363,373‧‧‧Switching device

364,365,374,375‧‧ ‧Switch

37‧‧‧Second communication module

First diagram (a): a circuit diagram showing a conventional half-duplex single transmission medium; first diagram (b): showing an equivalent circuit diagram of the first diagram (a); second diagram (a ): It shows a circuit diagram of a traditional full-duplex independent transmission medium; Second diagram (b): showing an equivalent circuit diagram of one of the second diagrams (a); and third diagram (a): showing a waveform of a transmission intensity corresponding to a transmission band of a conventional half-duplex single transmission system Figure 4 (a): shows the waveform of the transmission intensity corresponding to the transmission band of a traditional full-duplex independent transmission system; Figure 4 (b) shows the transmission amplitude of a traditional full-duplex independent transmission system Corresponding to the transmission time waveform diagram; FIG. 5 is a schematic diagram showing the architecture of an electronic signal transmission architecture according to a preferred embodiment of the present invention; and FIG. 6 is a preferred embodiment of the present invention. A first preferred embodiment of a first subsystem of the first high pass filter of the electronic signal transmission architecture of the example and a circuit diagram of a first preferred embodiment of a first subsystem of the first low pass filter FIG. 7(a) is a circuit diagram showing an analog circuit when using PSPICE to test an electronic signal transmission architecture according to a preferred embodiment of the present invention; and FIG. 7(b): showing the seventh An equivalent circuit diagram of one of the figures (a); and eighth : Which lines showed correlation waveform showing a simulation result of a full duplex transmission system according to the preferred embodiment of the contemplated embodiment of the present invention proposed.

3‧‧‧Electronic signal transmission architecture with full duplex single transmission medium

31‧‧‧First high-pass filter

32‧‧‧First low pass filter

33‧‧‧Second high-pass filter

34‧‧‧Second low pass filter

35‧‧‧Twisted pair cable

36‧‧‧First Communication Module

37‧‧‧Second communication module

Claims (20)

An electronic signal transmission architecture comprising: a single transmission medium having a first end and a second end, wherein a high speed signal and a low speed signal are simultaneously in the single transmission medium through a frequency separation manner The first end is connected to the second end; a first communication module; a first high-pass filter coupled to the first end and the first communication module, for transmitting or receiving the a high-speed signal; a first low-pass filter coupled to the first end and the first communication module for transmitting or receiving the low-speed signal; a second communication module; and a second high-pass filter The second terminal and the second communication module are configured to transmit or receive the high speed signal; and a second low pass filter is coupled to the second end and the second communication module. The low speed signal is transmitted or received. The architecture of claim 1, wherein the high speed signal and the low speed signal are transmitted in a frequency division multiplexing (FDD) manner. The architecture of claim 1, wherein the first and the second low-pass filters each have a low pass band, and the low-speed signal has a frequency in the low pass band. The first high-pass filter and the second high-pass filter each have a high pass band, and the high-speed signal has a frequency in the high-pass band. The architecture of claim 1, wherein the protection between the first and the second high pass filter and the first and second low pass filters The guard band is greater than 500KHz. The architecture of claim 1, wherein the ratio of the high speed signal to the low speed signal is greater than four. The architecture of claim 1, wherein each of the first and second high pass filters is selected from the group consisting of a Chebyshev high pass filter, a Butterworth high pass filter, and a Bessel high pass filter. Each of the first and second low pass filters is selected from any one of a Chebyshev low pass filter, a Butterworth low pass filter and a Bessel low pass filter. The architecture of claim 1, wherein the single transmission medium is one of four pairs of twisted pairs of a Category 5 (Cat5) cable. The first communication module is configured to receive the high-speed signal and transmit the low-speed signal, and the second communication module is used when the architecture is in a first state. Receiving the low speed signal and transmitting the high speed signal, and when the architecture is switched to a second state, the second communication module is configured to receive the high speed signal and transmit the low speed signal, and the first communication module is used Receiving the low speed signal and transmitting the high speed signal. The architecture of claim 8, wherein the switching between the first state and the second state is controlled via a software. The architecture of claim 8, wherein the switching between the first state and the second state is controlled via a switching device and at least one switch. Such as the structure described in claim 1 of the patent scope, wherein each of the first and the The second communication module further includes: a transmitter; and a receiver, wherein when the transmitter transmits the high speed signal, the receiver receives the low speed signal, and when the transmitter sends the low speed signal, the receiving The receiver receives the high speed signal. A multi-computer switcher (KVM) system electrically connecting a plurality of computers and a set of human interface devices, comprising: a switching device for switching a signal transmission path between the group of human interface devices and the computers; and a single transmission medium Having a first end and a second end, a high-speed signal and a low-speed signal are simultaneously transmitted between the first end and the second end of the single transmission medium through a frequency separation manner; a first high-pass filter coupled to the first end and the first communication module for transmitting or receiving the high-speed signal; a first low-pass filter coupled to the first And the first communication module is configured to transmit or receive the low speed signal; a second communication module; a second high pass filter coupled to the second end and the second communication module, Transmitting or receiving the high speed signal; and a second low pass filter coupled to the second end and the second communication module for transmitting or receiving the low speed signal. The system of claim 12, wherein the high speed signal The low speed signal is transmitted by a frequency division multiplexing (FDD) method. The system of claim 12, wherein the first and the second low pass filters each have a low pass band, and the frequency of the low speed signal is in the low pass band range. The first high-pass filter and the second high-pass filter each have a high pass band, and the high-speed signal has a frequency in the high-pass band. The system of claim 12, wherein a guard band between the first and second high pass filters and the first and second low pass filters is greater than 500 KHz, and The ratio of the high speed signal to the low speed signal frequency is greater than four. The system of claim 12, wherein the single transmission medium is one of four twisted pairs of a Category 5 (Cat5) cable. The system of claim 12, wherein, in a first state, the first communication module is configured to receive the high speed signal and transmit the low speed signal, and the second communication module is configured to receive the The low-speed signal transmits the high-speed signal, and when in the second state, the first communication module is configured to receive the low-speed signal and transmit the high-speed signal, and the second communication module is configured to receive the high-speed signal and The low speed signal is transmitted. The system of claim 12, wherein the switching between the first state and the second state is controlled via a switching device and at least one switch. A control method for a KVM system with a full duplex transmission architecture, wherein the KVM switch system is electrically connected A plurality of computers and a set of human interface devices are included. The KVM switch system includes a switching device for switching a signal transmission path between the set of human interface devices and the computers. The control method comprises the following steps: a) providing a single transmission medium having a first end and a second end, a high speed signal and a low speed signal; and (b) transmitting the high speed and the low speed signal by using a frequency division multiplexing (FDD) method. The high speed and the low speed signal can be simultaneously transmitted between the first end and the second end of the single transmission medium. The method of claim 19, further comprising the steps of: (c) providing a first high pass filter coupled to the first end and a first low pass filter, and coupled to the a second high pass filter and a second low pass filter; and (d) a pass band of the first and second high pass filters and the first and second low One of the pass filters has a guard band between the stop bands, wherein the guard band is the difference between the pass band and the stop band.