BACKGROUND Both two-way radio and cellular telephone products are becoming more sophisticated where they both can offer multiple modes of operation. These modes range from various modulation techniques, such as analog or digital, to multiple band operation, sometimes allowing the device to operate in portions of the radio spectrum that are literally GigaHertz apart in frequency. Under these circumstances it is necessary to switch amongst different components within the device that are specifically designed for these various modes of operation. For example, it might be necessary to switch between two different types of power amplifiers, i. e. one designed for digital operation and one designed for analog operation. Moreover, it might be necessary to switch different sections of an amplifier to enable operation over a wide frequency range and on multiple bands. In view of the cost and size constraints imposed upon most new products, it is necessary to provide a switch that can effectively accomplish this purpose using the fewest parts and occupying the least amount of space.

Thus, the need exists to provide an efficient low cost radio frequency switch that can be used to switch a two-way radio or cellular telephone between various modes of operation, such as when using an analog and/or digital power amplifier.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing the operation of the power amplifier transmit/receiver radio frequency switch used in the preferred embodiment of the invention.

FIG. 2 is a schematic diagram of the radio frequency switch shown in FIG. 1.

FIG. 3 is a schematic diagram of an alternative embodiment of the radio frequency switch shown in FIG. 1 allowing multiple frequency operation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, a block diagram of a three port radio frequency (RF) switch using a single quarter wave isolating section includes the antenna switch 101 that connects various inputs to an antenna port 103. Generally there are two power amplifier ports 105,107 and a receive port 109 that are used and switched independently to the antenna port 103. Although an analog RF power amplifier 105 and a digital RF power amplifier 107 are illustrated in FIGs. 1-3, it should be evident to those skilled in the art that the invention is not necessarily limited to analog and/or digital power amplifier applications but can be used for any number of general RF applications. The antenna switch 101, through the use of one or more control input (s) 111 can connect and isolate the analog RF power amplifier 105, digital RF power amplifier 107 or receiver 109 to the antenna port 103.

FIG. 2 illustrates a schematic diagram of the antenna switch 101 according to the preferred embodiment of the invention. The switch 101 includes the antenna port 103 that is switched between either a first amplifier port 105, a second amplifier port 107 or a receive port 109. As will be explained herein, the switch effectively switches and isolates the amplifier ports and receiver port from one another using only a minimum number of components.

This is accomplished using a number of control inputs 201,203 and 205 used to control a plurality of switching diodes. For example, the switching diode 207 is controlled through a signal input through a control line 201 that acts to bias the diode into either an open or closed state. Control line 203 provides control bias to switching diode 215 while control line 205 acts to bias and control switching diodes 213 and 215. Moreover, each control line 201,203,205 includes a choke or filter circuit 217, 219,221 respectively that connects serially to the input of each control line.

Each filter circuit includes a serial resister-inductor (RL) combination 219,221 acting to isolate the control ports from the desired RF signal. An inductor 209 is used to complete the DC path to ground while a coupling capacitor 211 is used to AC couple an RF signal from either the second port 107 or receive port 109 to the antenna port 103.

Further, an isolation circuit 220 includes a quarter wave isolating section 222 connected between the antenna port 103 and receive port 109. The isolating section 222 is frequency dependent and is selectively cut and/or sized to be one quarter wavelength (X/4) of the operating frequency. As will be evident to those skilled in the art, the isolating section 222 can be implemented with either discrete components (for

low frequency applications), microstrip transmission line or multilayer ceramic stripline with all discrete and active components on a top layer. Depending on the biased state of the switching diode 215, the isolating section 222 acts to either conduct or offer a high impedance to RF energy. This allows the isolating section 222 to effectively isolate RF energy from the receiver port 109, depending on the biased state of the switching diode 215.

Table 1 below illustrates the various bias states of the switching diodes 207, 213 and 215. By way of example, if switching diodes 207 and 215 are biased to an ON state and switching diode 213 is biased OFF, this would connect the first input port 105 to the antenna port 103. Similarly, if both switching diodes 213 and 215 are biased to an ON state, and switching diode 207 is biased OFF, this would switch the antenna port 103 to the second input port 107. If each of the switching diodes 207, 213 and 215 were biased OFF, then the antenna port 103 will be connected to the receive port 109.

Thus, it should be evident to those skilled in the art, that the present invention provides an easy means of switching two power amplifiers such as an analog and a digital power amplifier to an antenna port when in a transmit mode and where the antenna is subsequently returned to a receive port when in a receive mode. The invention can have a great amount of utility particularly in a dual mode type radio or cellular telephone where analog and digital modes are used with separate power amplifiers.

Table 1 Control Control Control Input Input Input 201 203 205 1 1 0 Amp Port 105 Ant 103 0 0 0 Ant Port 103 Rac 109 0 0 1 Amp Port 107 Ant 103 Where 1 = applied signal"ON"voltage and 0 = high impedance"OFF" An alternative embodiment of the invention is illustrated in FIG. 3, where a similar type of isolating circuit 220'includes a plurality of diode switches used to

switch the first amplifier port 105, a second amplifier port 107 and receiver port 109 to an antenna port 103. This embodiment is useful in situations were it is necessary to accommodate large splits in radio frequency for"multiband"operations. As is well known in the art, multiband operations are those modes where more than one frequency band is used, such as very high frequency (VHF) and ultra high frequency (UHF). In this embodiment it is necessary to use different lengths of quarter wave isolating sections in view of their specific frequency characteristics. This can be accomplished using an additional diode switch 303 with control line 201'. As illustrated in Table 2, control line 201,201'serves a dual role by controlling both switching diode 207 as well as switching diode 303.

Table 2

Where 1 = applied signal"ON"voltage and 0 = high impedance"OFF".

Frequency F, < Frequency F2 Hence, by biasing the appropriate switching diode a specific isolating section 217 or 217'can be selected allowing different lengths of quarter wave matching section 217,217'within the switch to operate over a wide frequency range. As will be evident to those of ordinary skill, any number of isolating sections can be selected using the appropriate number of switching diodes. This embodiment also illustrates where the frequency at input 105 is less than the frequency at input 107. Accordingly the control input 201 can also be used to control the control input 201'allowing for the switch to operate not only with one switching isolating section but also with an additional isolating section 217'for use in situations where a wide frequency range is needed such as in multiband or wide frequency operations.

In short, the present invention can be used to efficiently switch an antenna port between three input ports such as two amplifier ports and a receiver port in a two-way communications device over both narrow and wide frequency ranges. It is compact, inexpensive and utilizes one or more quarter wave isolating sections for switching various input ports to an antenna port.

While the preferred embodiments of the invention have been illustrated and described, it will be clear that the invention is not so limited. Numerous modifications, changes, variations, substitutions and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims.

What is claimed is: