Switchable filtering circuit and the operation method using the same

The disclosure provides a switchable filtering circuit and the related operation method, in particular related to a filtering circuit which can be used for Bluetooth system and wireless local area network system. By using a first switch, a hybrid filtering circuit and a second switch, the received mode and transmitted mode between these two systems is realized. Moreover, the frequency responses and the bandwidth adjustments can be controlled according to the plurality of switchable resistors, the plurality of switchable capacitors and the shared and switchable resistors within the hybrid filter circuit. Moreover, the effects of high operated freedom of the circuit and the circuit size reduction can be achieved.

TECHNICAL FIELD

The disclosure relates to a filtering circuit and the operation method using the same, and in particular to a switchable filtering circuit for receiving and transmitting the signals of Bluetooth system and wireless local area network system.

BACKGROUND

The filter design plays an important role in the communication system. An ideal received filter can minimize the distortion of the signals and filter the interference out of band to achieve the maximum signal-to-noise ratio (SNR), and an acceptable bandwidth-limitation. However, the purpose of minimizing the distortion exhibits some conflicts with that of filtering the noise and the interference completely. Therefore, design of the received filters has to make a balance between the distortion and the noise.

On the other hand, the transmitted filter is used to make the bandwidth of the transmitted signal satisfy the standard in the specific spectrum. Because the transmitted signal for the digital communication is generated from a digital-to-analog converter, the transmitted filter should be designed to remove the harmonic which is generated from the operation of sample and hold of the digital-to-analog converter. In the design of the transmitted filter, the requirements for removing harmonic are decided according to the characteristics of the digital-to-analog converter, such as sampling frequency. Due to the rebuilding operation of the transmitted filter for the analog waveform (trapezoid) of the digital-to-analog converter, the transmitted filter is named as rebuilding filter as well.

Bandwidth is the most parameter for the filter design. In the conventional communication system, the bandwidth of the transmitted filter is larger than the bandwidth of the received filter. Therefore, in order to optimize the efficiency of the received filter and the transmitted filter, separable transmitted filter and separable received filter are adopted in the design of the recent transceiver. However, due to the independence of the separable transmitted filter and the separable received filter, more time is spent to switch the transmitted mode and the received mode, and the size of the transmitter and the cost of the products are also increased.

FIG. 1shows a common system of the filtering circuit of the transmitted port and the received port in the prior invention. The filtering circuit switches the transmitted mode and the received mode to minimize circuit size through the plural switches. However, the filtering circuit is not suitable for the distinct systems.

U.S. Pat. No. 2007/0040605 A1 discloses a shared receiver and transmitter filter. In order to share the filters, the invention adopts four switches into the received circuit and the transmitted circuit to switch the transmitted mode and the received mode. However, the disclosed filter is merely suitable for the common system of the circuit of the transmitted port and the received port.

According to the above discussions, it need an apparatus and a method to overcome the disadvantage of the prior art.

SUMMARY

It is an objective of the disclosure to provide a switchable filtering circuit. The circuit can be used in the received mode and the transmitted mode for the Bluetooth system and the wireless local area network system, and can be used to decide the frequency response and the passband bandwidth for the hybrid filter.

It is another objective of the disclosure to provide an operated method of the switchable filtering circuit.

To achieve the above objective, the disclosure provides a switchable filtering circuit, in particular to the wireless local area network system and the Bluetooth system. The switchable filtering circuit comprises: a first switch, a hybrid filtering circuit, a second switch. The first switch has a first input port, a second input port, a third input port, a fourth input port, a first output port, a second output port, a third output port and a fourth output port, the first input port is electrically connected to an output port of a RF circuit of a first receiver, the second input port is electrically connected to an output port of a baseband circuit of a first transmitter, the third input port is electrically connected to an output port of a RF circuit of a second receiver, and the fourth input port is electrically connected to an output port of a baseband circuit of a second transmitter. The hybrid filtering circuit has a first input port, a second input port, a third input port, a fourth input port, a first output port, a second output port, a third output port and a fourth output port, the first input port is electrically connected to the first output port of the first switch, the second input port is electrically connected to the second output port of the first switch, the third input port is electrically connected to the third output port of the first switch, the fourth input port is electrically connected to the fourth output port of the first switch. The second switch has a first input port, a second input port, a third input port, a fourth input port, a first output port, a second output port, a third output port and a fourth output port, the first input port is electrically connected to the first output port of the hybrid filtering circuit, the second input port is electrically connected to the second output port of the hybrid filtering circuit, the third input port is electrically connected to the third output port of the hybrid filtering circuit, the fourth input port is electrically connected to the fourth output port of the hybrid filtering circuit, the first output port is electrically connected to a first input port of a baseband circuit of a first receiver, the second output port is electrically connected to an input port of a RF circuit of a first transmitter, the third output port is electrically connected to an input port of a baseband circuit of a second receiver, and the fourth output port electrically connected to an input port of a RF circuit of a second transmitter.

To achieve another objective, the disclosure provides an operation method of switchable filtering circuit, particularly used for wireless local area network system and Bluetooth system. The operation method comprises steps of: step 1: when the switchable filtering circuit as claimed in claim1is set as received mode for a wireless local area network system, connecting the output port of the RF circuit of the first receiver to the first input port of the first switch, connecting the first output port of the first switch to the input port of the first switchable resistor, connecting the first input port of the second switch to the first output port of the first amplifier, and connecting the first output port of the second switch to the input port of the baseband circuit of the first receiver; step 2: when the switchable filtering circuit as claimed in claim1is set as transmitted mode for a wireless local area network system, connecting the output port of the baseband circuit of the first transmitter to the second input port of the first switch, connecting the second output port of the first switch to the input port of the second switchable resistor, connecting the second input port of the second switch to the second output port of the first amplifier, and connecting the second output port of the second switch to the input port of the RF circuit of the first transmitter; step 3: when the switchable filtering circuit as claimed in claim1is set as received mode for a Bluetooth system, connecting the output port of the RF circuit of the second receiver to the third input port of the first switch, connecting the third output port of the first switch to the input port of the fifth switchable resistor, connecting the third input port of the second switch to the first output port of the second amplifier, and connecting the third output port of the second switch to the input port of the baseband circuit of the second receiver; step 4: when the switchable filtering circuit as claimed in claim1set as transmitted mode for a Bluetooth system, connecting the output port of the baseband circuit of the second transmitter to the fourth input port of the first switch, connecting the fourth output port of the first switch to the input port of the sixth switchable resistor, connecting the fourth input port of the second switch to the second output port of the second amplifier, and connecting the fourth output port of the second switch to the input port of the RF circuit of the second transmitter.

To sum up the above disclosures, the switchable filtering circuit and the operation method using the same according to the invention presents the following advantages:

1. Shared filter for the Bluetooth system and wireless local area network system is used to reduce circuit size and cost.

2. By using the switches with the switchable resistors and the plurality of switchable capacitors to determine the on/off status of the plurality of switchable resistors and switchable capacitors, the frequency responses and the bandwidth adjustments can be controlled and the effects of high operated freedom of the circuit and the circuit size reduction can be achieved.

These and many other advantages and features of the disclosure will be readily apparent to those skilled in the art from the following drawings and detailed descriptions.

DETAILED DESCRIPTION

Although the invention has been explained in relation to several preferred embodiments, the accompanying drawings and the following detailed descriptions are the preferred embodiment of the disclosure. It is to be understood that the following disclosed descriptions will be examples of disclosure, and will not limit the disclosure into the drawings and the special embodiment.

To understand the spirit of the disclosure,FIG. 2shows a switchable filtering circuit100, in particular to the wireless local area network system and the Bluetooth system. The switchable filtering circuit100mainly comprises: a first switch141, a hybrid filtering circuit130, a second switch142.

The first switch141has a first input port, a second input port, a third input port, a fourth input port, a first output port, a second output port, a third output port and a fourth output port, the first input port is electrically connected to an output port of a RF circuit of a first receiver110, the second input port is electrically connected to an output port of a baseband circuit of a first transmitter111, the third input port is electrically connected to an output port of a RF circuit of a second receiver121, and the fourth input port is electrically connected to an output port of a baseband circuit of a second transmitter120.

The hybrid filtering circuit130has a first input port, a second input port, a third input port, a fourth input port, a first output port, a second output port, a third output port and a fourth output port, the first input port is electrically connected to the first output port of the first switch141, the second input port is electrically connected to the second output port of the first switch141, the third input port is electrically connected to the third output port of the first switch141, the fourth input port is electrically connected to the fourth output port of the first switch141.

The second switch142has a first input port, a second input port, a third input port, a fourth input port, a first output port, a second output port, a third output port and a fourth output port, the first input port is electrically connected to the first output port of the hybrid filtering circuit130, the second input port is electrically connected to the second output port of the hybrid filtering circuit130, the third input port is electrically connected to the third output port of the hybrid filtering circuit130, the fourth input port is electrically connected to the fourth output port of the hybrid filtering circuit130, the first output port is electrically connected to a first input port of a baseband circuit of a first receiver112, the second output port is electrically connected to an input port of a RF circuit of a first transmitter113, the third output port is electrically connected to an input port of a baseband circuit of a second receiver122, and the fourth output port is electrically connected to an input port of a RF circuit of a second transmitter123.

The hybrid filtering circuit130comprises: a first switchable resistor1311, a second switchable resistor1312, a first amplifier1331, a first switchable capacitor1321, a third switchable resistor1313, a second switchable capacitor1322, a fourth switchable resistor1314, a fifth switchable resistor1315, a sixth switchable resistor1316, a second amplifier1332, a third switchable capacitor1323, a seventh switchable resistor1317, a fourth switchable capacitor1324, a eighth switchable resistor1318, a plurality of array of shared and switchable resistors1340.

Wherein, the first switchable resistor1311has an input port and an output port, the input port is electrically connected to the first output port of the first switch141. The second switchable resistor1312has an input port and an output port, the input port is electrically connected to the second output port of the first switch141. The first amplifier1331has a first input port, a second input port, a first output port and a second output port, the first input port is electrically connected to the output port of the first switchable resistor1311, and the second input port is electrically connected to the output port of the second switchable resistor1312. The first switchable capacitor1321has an input port and an output port, the input port is electrically connected to the first input port of the first amplifier1331, and the output port is electrically connected to the first output port of the first amplifier1331. The third switchable resistor1313has an input port and an output port, the input port is electrically connected to the first input port of the first amplifier1331, and the output port is electrically connected to the first output port of the first amplifier1331. The second switchable capacitor1322has an input port and an output port, the input port is electrically connected to the second input port of the first amplifier1331, and the output port is electrically connected to the second output port of the first amplifier1331. The fourth switchable resistor1314has an input port and an output port, the input port is electrically connected to the second input port of the first amplifier1331, and the output port is electrically connected to the second output port of the first amplifier1331. The fifth switchable resistor1315has an input port and an output port, the input port is electrically connected to the third output port of the first switch141. The sixth switchable resistor has an input port and an output port, the input port is electrically connected to the fourth output port of the first switch141. The second amplifier1332has a first input port, a second input port, a first output port and a second output port, the first input port is electrically connected to the output port of the fifth switchable resistor1315, and the second input port is electrically connected to the output port of the sixth switchable resistor1316. The third switchable capacitor1323has an input port and an output port, the input port is electrically connected to the first input port of the second amplifier1332, and the output port is electrically connected to the first output port of the second amplifier1332. The seventh switchable resistor1317has an input port and an output port, the input port is electrically connected to the first input port of the second amplifier1332, and the output port is electrically connected to the first output port of the second amplifier1332. The fourth switchable capacitor1314has an input port and an output port, the input port is electrically connected to the second input port of the second amplifier1332, and the output port is electrically connected to the second output port of the second amplifier1332. The eighth switchable resistor1318has an input port and an output port, the input port is electrically connected to the second input port of the second amplifier1332, and the output port is electrically connected to the second output pot of the second amplifier1332. The plurality of array of shared and switchable resistors1340has a first input port, a second input port, a third input port, a fourth input port, a first output port, a second output port, a third output port and a fourth output port, the first input port is electrically connected to the output port of the first switchable resistor1311, the second input port is electrically connected to the output port of the second switchable resistor1312, the third input port is electrically connected the output port of the fifth switchable resistor1315, the fourth input port is electrically connected to the output port of the sixth switchable resistor1316, the first output port electrically connected to the first output port of the first amplifier1331, the second output port is electrically connected to the second output port of the first amplifier1331, the third output port is electrically connected to the first output port of the second amplifier1332, and the fourth output port is electrically connected to the second output port of the second amplifier1332. Wherein the first switchable resistor1311, the second switchable resistor1312, the third switchable resistor1313, the fourth switchable resistor1314, the fifth switchable resistor1315, the sixth switchable resistor1316, the seventh switchable resistor1317, the eighth switchable resistor1318, the first switchable capacitor1321, the second switchable capacitor1322, the third switchable capacitor1323and the fourth switchable capacitor1324all have a switch for each other. The corresponding switches determine the on/off statuses of the first switchable resistor1311, the second switchable resistor1312, the third switchable resistor1313, the fourth switchable resistor1314, the fifth switchable resistor1315, the sixth switchable resistor1316, the seventh switchable resistor1317, the eighth switchable resistor1318, the first switchable capacitor1321, the second switchable capacitor1322, the third switchable capacitor1323and the fourth switchable capacitor1324.

In addition, the plurality of array of shared and switchable resistors1340comprises: a first shared and switchable resistor1341, a second shared and switchable resistor1342, the third shared and switchable resistor1343, a fourth shared and switchable resistor1344. The first shared and switchable resistor1341has an input port and an output port, the input port is electrically connected to the output port of the first switchable resistor1311, and the output port is electrically connected to the first output port of the first amplifier1331. The second shared and switchable resistor1342has an input port and an output port, the input port is electrically connected to the output port of the second switchable resistor1312, and the output port is electrically connected to the second output port of the first amplifier1331. The third shared and switchable resistor1343has an input port and an output port, the input port is electrically connected to the output port of the fifth switchable resistor1315, and the output port is electrically connected to the first output port of the second amplifier1332. The fourth shared and switchable resistor1344, having an input port and an output port, the input port is electrically connected to the output port of the sixth switchable resistor1316, and the output port is electrically connected to the second output port of the second amplifier1332. Wherein the first shared and switchable resistor1341, the second shared and switchable resistor1342, the third shared and switchable resistor1343and the fourth shared and switchable resistor1344all have a switch for each other. The corresponding switches determine the on/off statuses of the first shared and switchable resistor1341, the second shared and switchable resistor1342, the third shared and switchable resistor1343and the fourth shared and switchable resistor1344.

In general, the hybrid filtering circuit130can be formed as a high-stage filtering circuit by cascading the hybrid filtering circuit130constantly. However, the resistance values of the first switchable resistor1311, the resistance values of the second switchable resistor1312, the resistance values of the third switchable resistor1313and the resistance values of the fourth switchable resistor1314equal to each other. The capacitance values of the first switchable capacitor1321and the capacitance values of the second switchable capacitor1322equal to each other. The resistance values of the fifth switchable resistor1315, the resistance values of the sixth switchable resistor1316, the resistance values of the seventh switchable resistor1317and the resistance values of the eighth switchable resistor1318equal to each other. The capacitance values of the third switchable capacitor1323and the capacitance values of the fourth switchable capacitor1324equal to each other. The resistance values of the first shared and switchable resistor1341, the resistance values of the second shared and switchable resistor1342, the resistance values of the third shared and switchable resistor1343and the resistance values of the fourth shared and switchable resistor1344equal to each other.

The adopted filter of the disclosure is formed as an active filter through an operational amplifier, a feedback resistor array and a feedback capacitor array. Note also here, the disclosure also discloses a shared and switchable resistor array to satisfy the operation of the dual-system simultaneously.

For the characteristic of the active filter, when the hybrid filtering circuit130is set as a low-pass filter, the passband bandwidth of the low-pass filter defined according to the reciprocal of the product of the values of the resistance from the first switchable resistor1311, the second switchable resistor1312, the third switchable resistor1313and the fourth switchable resistor1314and the values of the capacitance from the first switchable capacitor1321and the second switchable capacitor1322. When the hybrid filtering circuit130is set as a bandpass filter, the passband bandwidth of the bandpass filter defined according to the reciprocal of the product of the values of the resistance from the first shared and switchable resistor1311, the second shared and switchable resistor1312, the third shared and switchable resistor1313and the fourth shared and switchable resistor1314and the values of the capacitance from the first switchable capacitor1321and the second switchable capacitor1322.

FIG. 3shows a functional block diagram for an embodiment of the switchable filtering circuit of the disclosure. The RF circuit of the first receiver110and the baseband circuit of the first transmitter111are the RF front-end receiver and transmitter for the wireless local area network system, respectively, and the RF circuit of the second receiver121and the baseband circuit of the second transmitter120are the RF front-end receiver and transmitter for the Bluetooth system, respectively. For the embodiment, three-stage filter is used for Bluetooth system, and five-stage filter is used for wireless local area network system, however, the above three-stage and five-stage filter can be built by cascading two hybrid filtering circuit130and four hybrid filtering circuit130, respectively. Note also here, due to the high-stage filter for the wireless local area network system, a third switch is used to switch the operated mode after cascading four hybrid filtering circuit130. In addition, the bandwidth of the hybrid filtering circuit130is set as 5 MHz, 10 MHz or 20 MHz for the wireless local area network system, and exhibits a bandwidth range from 600 KHz to 1 MHz for Bluetooth system.

To further understand the spirit of the disclosure, an operation method of the switchable filtering circuit is provided, particularly used for wireless local area network system and Bluetooth system, wherein comprising steps of:

step 1: when the switchable filtering circuit100is set as received mode for a wireless local area network system, connecting the output port of the RF circuit of the first receiver110to the first input port of the first switch141, connecting the first output port of the first switch141to the input port of the first switchable resistor1311, connecting the first input port of the second switch142to the first output port of the first amplifier1331, and connecting the first output port of the second switch142to the input port of the baseband circuit of the first receiver112; step 2: when the switchable filtering circuit100is set as transmitted mode for a wireless local area network system, connecting the output port of the baseband circuit of the first transmitter111to the second input port of the first switch141, connecting the second output port of the first switch141to the input port of the second switchable resistor1312, connecting the second input port of the second switch142to the second output port of the first amplifier1331, and connecting the second output port of the second switch142to the input port of the RF circuit of the first transmitter113; step 3: when the switchable filtering circuit100is set as received mode for a Bluetooth system, connecting the output port of the RF circuit of the second receiver121to the third input port of the first switch141, connecting the third output port of the first switch141to the input port of the fifth switchable resistor1315, connecting the third input port of the second switch142to the first output port of the second amplifier1332, and connecting the third output port of the second switch142to the input port of the baseband circuit of the second receiver122; and step 4: when the switchable filtering circuit100is set as transmitted mode for a Bluetooth system, connecting the output port of the baseband circuit of the second transmitter120to the fourth input port of the first switch141, connecting the fourth output port of the first switch141to the input port of the sixth switchable resistor1316, connecting the fourth input port of the second switch142to the second output port of the second amplifier1332, and connecting the fourth output port of the second switch142to the input port of the RF circuit of the second transmitter123.

When the hybrid filtering circuit130is set as a low-pass filter, the step further comprises the steps of:

step 1-1: when setting as received mode for a wireless local area network system, turning on the first shared and switchable resistor1341, the second shared and switchable resistor1342, the third shared and switchable resistor1343and the fourth shared and switchable resistor1344within the plurality of array of shared and switchable resistors1340, turning on one of the first switchable capacitor1321and the second switchable capacitor1322, and turning on one of the first switchable resistor1311, the second switchable resistor1312, the third switchable resistor1313and the fourth switchable resistor1314; step 2-1: when setting as transmitted mode for a wireless local area network system, turning on the first shared and switchable resistor1341, the second shared and switchable resistor1342, the third shared and switchable resistor1343and the fourth shared and switchable resistor1344within the plurality of array of shared and switchable resistors1340, turning on one of the first switchable capacitor1321and the second switchable capacitor1322, and turning on one of the first switchable resistor1311, the second switchable resistor1312, the third switchable resistor1313and the fourth switchable resistor1314; step 3-1: when setting as received mode for a Bluetooth system, turning on the first shared and switchable resistor1341, the second shared and switchable resistor1342, the third shared and switchable resistor1343and the fourth shared and switchable resistor1344within the plurality of array of shared and switchable resistors1340, turning on one of the third switchable capacitor1323and the fourth switchable capacitor1324, and turning on one of the fifth switchable resistor1315, the sixth switchable resistor1316, the seventh switchable resistor1317and the eighth switchable resistor1318; and step 4-1: when setting as transmitted mode for a Bluetooth system, turning on the first shared and switchable resistor1341, the second shared and switchable resistor1342, the third shared and switchable resistor1343and the fourth shared and switchable resistor1344within the plurality of array of shared and switchable resistors1340, turning on one of the third switchable capacitor1323and the fourth switchable capacitor1324, and turning on one of the fifth switchable resistor1315, the sixth switchable resistor1316, the seventh switchable resistor1317and the eighth switchable resistor1318.

When the hybrid filtering circuit130is set as a bandpass filter, the step further comprises the steps of:

step 1-1: when setting as received mode for a wireless local area network system, turning on the first shared and switchable resistor1341, the second shared and switchable resistor1342, the third shared and switchable resistor1343and the fourth shared and switchable resistor1344within the plurality of array of shared and switchable resistors1340, turning on one of the first switchable capacitor1321and the second switchable capacitor1322, and turning on one of the first switchable resistor1311, the second switchable resistor1312, the third switchable resistor1313and the fourth switchable resistor1314; step 2-1: when setting as transmitted mode for a wireless local area network system, turning on the first shared and switchable resistor1341, the second shared and switchable resistor1342, the third shared and switchable resistor1343and the fourth shared and switchable resistor1344within the plurality of array of shared and switchable resistors1340, turning on one of the first switchable capacitor1321and the second switchable capacitor1322, and turning on one of the first switchable resistor1311, the second switchable resistor1312, the third switchable resistor1313and the fourth switchable resistor1314; step 3-1: when setting as received mode for a Bluetooth system, turning on the first shared and switchable resistor1341, the second shared and switchable resistor1342, the third shared and switchable resistor1343and the fourth shared and switchable resistor1344within the plurality of array of shared and switchable resistors1340, turning on one of the third switchable capacitor1323and the fourth switchable capacitor1324, and turning on one of the fifth switchable resistor1315, the sixth switchable resistor1316, the seventh switchable resistor1317and the eighth switchable resistor1318; and step 4-1: when setting as transmitted mode for a Bluetooth system, turning on the first shared and switchable resistor1341, the second shared and switchable resistor1342, the third shared and switchable resistor1343and the fourth shared and switchable resistor1344within the plurality of array of shared and switchable resistors1340, turning on one of the third switchable capacitor1323and the fourth switchable capacitor1324, and turning on one of the fifth switchable resistor1315, the sixth switchable resistor1316, the seventh switchable resistor1317and the eighth switchable resistor1318.

FIG. 4shows a functional block diagram for another embodiment of the circuit operation of the switchable filtering circuit of the disclosure. For the embodiment, three-stage filter is used for Bluetooth system, and five-stage filter is used for wireless local area network system, however, the above three-stage and five-stage filter can be built by cascading two hybrid filtering circuit130and four hybrid filtering circuit130, respectively. Note also here, due to the high-stage filter for the wireless local area network system, a third switch is used to switch the operated mode after cascading four hybrid filtering circuit130.

FIG. 4.(a) shows that when the switchable filtering circuit100is set as received mode for a wireless local area network system, the output port of the RF circuit of the first receiver110is electrically connected to the first input port of the first switch141, the first output port of the first switch141is electrically connected to the input port of the first switchable resistor1311, the first input port of the second switch142is electrically connected to the first output port of the first amplifier1331, and the first output port of the second switch142is electrically connected to the input port of the baseband circuit112of the first receiver;

FIG. 4.(b) shows that when the switchable filtering circuit100is set as transmitted mode for a wireless local area network system, the output port of the baseband circuit of the first transmitter111is electrically connected to the second input port of the first switch141, the second output port of the first switch141is electrically connected to the input port of the second switchable resistor1312, the second input port of the second switch142is electrically connected to the second output port of the first amplifier1331, and the second output port of the second switch142is electrically connected to the input port of the RF circuit113of the first transmitter;

FIG. 4.(c) shows that when the switchable filtering circuit100is set as received mode for a Bluetooth system, the output port of the RF circuit of the second receiver121is electrically connected to the third input port of the first switch141, the third output port of the first switch141is electrically connected to the input port of the fifth switchable resistor1315, the third input port of the second switch142is electrically connected to the first output port of the second amplifier1332, and the third output port of the second switch142is electrically connected to the input port of the baseband circuit122of the second receiver; and

FIG. 4.(d) shows that when the switchable filtering circuit100is set as transmitted mode for a Bluetooth system, the output port of the baseband circuit of the second transmitter120is electrically connected to the fourth input port of the first switch141, the fourth output port of the first switch141is electrically connected to the input port of the sixth switchable resistor1316, the fourth input port of the second switch142is electrically connected to the second output port of the second amplifier1332, and the fourth output port of the second switch142is electrically connected to the input port of the RF circuit123of the second transmitter.

Note also here, the transistors of above active circuit can be implemented by using 0.18 .mu.m, 0.13 .mu.m, 0.09 .mu.m, 0.0045 .mu.m, or more advanced process, wherein the transistor can be implemented as: Bipolar Junction Transistor (BJT), Heterojunction Bipolar Transistor (HBT), High Electronic Mobility Transistor (HEMT), Pseudomorphic HEMT (PHEMT), Complementary Metal Oxide Semiconductor Filed Effect Transistor (CMOS) and Laterally Diffused Metal Oxide Semiconductor Filed Effect Transistor (LDMOS). Preferably, PHEMT is suitable for the gain stage and power stage in the microwave to millimeter wave range. Semiconductor materials broadly applicable to the gain stage and power stage include: silicon, silicon-on-insulator (SOI), silicon-germanium (SiGe), gallium arsenide (GaAs), indium phosphide (InP) and silicon-germanium-carbon (SiGe—C) materials.

Although the invention has been explained in relation to its preferred embodiment, it is not used to limit the invention. It is to be understood that many other possible modifications and variations can be made by those skilled in the art without departing from the spirit and scope of the invention as hereinafter claimed.