Title of Invention

"A HIGH SPEED AND HIGH POWER SINGLE POLE SIXTEEN THROW PIN DIODE SWITCH"

Abstract

A High Speed and High Power Single Pole Sixteen Throw Pin Diode Switch A single pole sixteen throw PIN diode (SP16T) switch for microwave applications having capability to switch the input to any one of the sixteen output ports characterized by a cascading of one high power single pole double throw (SP2T) switch, the said SP2T switch has three shunt diodes in each arm for getting isolation, two single pole eight throw (SP8T) switches and a driver circuit means; the said SP2T switch having silicon PIN diodes using all shunt configuration; the said SP8T switches utilising series shunt configuration, wherein the series devices are in the low-impedance (inducative) state and shunt devices are in the high impedance (capacitive) state.

Full Text

FIELD OF INVENTION: This invention relates to a high power and fast routing single pole sixteen throw PIN diode switch for microwave applications. PRIOR ART: Routing switches are utilised in microwave systems/subsystems for routing microwave power. In any switching operation, it is desirable to have switches which are fast, have low loss and which can handle high power. One of the earliest types of routing switches, known in art, are electro mechanical switches. However, these switches suffer from the following disadvantages •Main disadvantage of the electromechanical switches, known in the prior art, is that the switches can not be used for more than 105 connections. Another disadvantage of the electromechanical switches, known in the prior art, is that the life time of these switches is limited Yet another disadvantage of these electromechanical switches, known in the prior art, is that the switches are bulky and these are not reliable Still further disadvantage of the electromechanical switches known in tne prior art, is that it is difficult to realise multi-port configuration for microwave applications. Yet further disadvantage of the electromechanical switches, known in the prior art, is that these switches have switching time of the order of milli second Ferrite switches are another type of switches, which can be used for high power broadband microwave applications. Although the switches have improved characteristics over the earlier mentioned electromechanical switches as tnese are less complex and less bulky, these switches also suffer from the following disadvantages. Main disadvantage of the ferrite switches, known in the art. is that the switches are temperature sensitive and their characteristics vary with the change in the ambient temperature. Another disadvantage of the ferrite switches, known in the prior art. is that the switches require high current drivers for switching operations Still further disadvantage of the ferrite switches, known in the prior art. is that it is difficult to realize multi-port configuration for microwave applications Yet further disadvantage of the ferrite switches, known in the prior art, is that these switches are also quite bulky. Still further disadvantage of the ferrite switches, known in the prior art, is that these switches have switching speed of the order of milli second. Monolithic Microwave Integrated Switches (MMIC) are the latest technology switches offering many improved characteristics over the electromechanical as well as ferrite switches for broad band microwave applications. As the switches are based on MMIC technology, all the circuit elements and semiconductors are realised in the same wafer. The switches are extremely compact and lightweight. Further, the switches also have switching speed of the order of nano second. However, even the MMIC switches, due to the inherent characteristics of MMIC technology, suffer from following disadvantages when used for multi-port switches for high power broadband microwave applications. Main disadvantage of the MMIC switches, known in the prior art, is that switches can not handle high power of the order of+33 dBm in the multi-port configuration Another disadvantage of the MMIC multi-port switches, known in the prior art, is that the switches can not provide high isolation in the multi-port configuration due to the lack of physical isolation between the ports. A PIN diode is a microwave semiconductor diode, which can be used as an electronically variable resistor The semiconductor wafer has heavily doped p+ region and a heavily doped n+ region separated by lightly doped high resistivity intrinsic layer depending upon whether the type of conductivity is p or n respectively. PIN diode switches provide state-of-the-art switching performance in most present day microwave and millimeter-wave systems. Their unique characteristics make them best choice for a wide variety of control applications, such as switches, attenuators, phase shifters, limiters, and modulators. PIN diodes can be incorporated in wave-guide, coaxial, strip-line and micro-strip transmission mediums for realisation of control circuits. PIN diode switches have high reliability and superior switching performance compared to electromechanical switches and ferrite switches PIN diode switches outperform even MMIC switches in their power handling and multi-port capability. DESCRIPTION OF INVENTION According to this invention there is provided A single pole sixteen throw PIN diode (SP16T) switch for microwave applications having capability to switch the input to any one of the sixteen output ports and comprising: A cascading of one high power single pole double throw (SP2T) switch, two single pole eight throw (SP8T) switches and a driver circuit means; the said SP2T switch having silicon PIN diodes using all shunt configuration, the said SP8T switches utilising series shunt configuration, wherein the series devices are in the low-impedance (inducative) state and shunt devices are in the high impedance (capacitive) state DESCRIPTION OF THE DRAWINGS: Any further characteristics, advantages and applications of the invention will become evident from the detailed description of the preferred embodiment which has been described and illustrated with the help of following drawings wherein, Fig 1 is the schematic diagram of SP16T switch of the present invention. Fig 2 is the schematic diagram of SP16T switch of the present invention comprising SP2T and SP8T switches Fig 3 is the schematic diagram showing all shunt diode configuration of the SP2T switch used in SP16T switch of the present invention Fig 4 is the schematic diagram of series shunt configuration of the SP8T switch used in the SP16T switch of the present invention Fig 5 is the schematic diagram of driver circuit used for the SP16T switch of the present invention. The SP8T switch (single pole eight throw) of the present invention utilises a series-shunt configuration, which provides improved bandwidth as well as high isolation. The basic concept involves the use of a ladder network structure that behaves like a low-pass filter when series devices are in the low-impedance (inductive) state and shunt devices are in the high impedance (capacitive) state, and when the bias states on the series-shunt switching devices are interchanged, the network behaves as a high pass filter providing a high insertion loss below the cut-off frequency. Referring to the figures 1, the SP16T switch (single pole sixteen throw) comprises sixteen output ports and it can switch the input to any of the sixteen output ports. • Referring to Fig. 2, the SP16T (single pole sixteen throw) switch comprises cascading of one high power SP2T switch and two SP8T switches with simultaneous switching waveform generation driver. The SP2T switch uses all shunt configuration and the diodes used are silicon PIN diodes, which can withstand the high input CW power. The bias circuit design generates the required voltages and currents to both SP2T and SP8T switches to enable simultaneous switching, a mandatory requirement to get fast switching speed. Referring to Fig. 3, the SP2T switch uses three shunt diodes in each arm to get the required isolation. The bandwidth of the switch is improved by a simple impedance matching technique. A third transmission line, a quarter wavelength at for is placed between the common junction and the input port In addition, the impedance (Z) of all the three lines is set to some value below 50 ohms The specific value of impedance that is chosen will determine the VSWR (Voltage Standing Wave Ratio) and the bandwidth of the switch. Setting the impedance of the three transmission lines to 35 ohms results in a 1.43:1 VSWR and banawidtn of 100%. The shunt diode configuration is generally used when switching speec and high power handling are of paramount consideration. Referring to Fig. 4, the SP8T switch utilises series shunt configuration Once the input power is reduced by about 2.5 to 3.0 dB by the insertion loss of the SP2T switch (from +33 dBm to +30 dBm), the +30dBm power level can be easily handled by the series shunt configuration of the SP8T switch As the number of throws increases, the common junction of the multi port switch becomes crowded by the series diodes. The technique used to overcome this limitation is cascading the SP16T switch by joining two SP8T switches with a SP2T switch. This approach was followed in the design as this avoids the physical crowding of the series diodes and the coupling between the adjacent arms of the multi port switch if the physical separation between them at tne common junction is small. The capacitance of the diode determines the upper frequency limit up to. which it can be used as a shunt element across a transmission line with tolerable VSWR. A frequently used method to overcome this limitation is by incorporating the capacitance of the diode Cj into a low pass filter that is matched on both sides. Micro-strip line is chosen as the transmission medium for the switch. A microstrip line consists of a single thin center conductor separated from the ground plane by means of a dielectric having a height 'h' and dielectric constant The dielectric above the center conductor is air. This results in an inhomogeneous transmission medium with RF energy propagating mostly in the dielectric and a small fraction in the air. The choice of the proper transmission medium, the selection of appropriate circuit topology and PIN diode are the key factors in the development of multi-port switch. For solid-state control components operating over wide bandwidth at medium power levels, micro strip is the most suitable transmission medium. Microstrip being a planar transmission medium, discrete semiconductor chip devices like PIN diodes and other circuit elements like dc block, RF choke and RF bypass can be easily assembled and integrated using standard bonding techniques. The thickness of the substrate chosen is quite compatible with the thickness of the commercially available PIN diode chips and allows the line width for easy transition to coaxial launchers like RF connectors. Sizes of the biasing elements are kept as small as possible so that the properties of the lumped circuit are utilized to the maximum. It is preferable to have the shunt diodes with lower Cj and lower RF and in miniature chip form with ribbon leads so that they can be easily incorporated in the low pass filter structure. It is desirable to have beam lead diodes for series application as beam lead diodes offer the lowest capacitance. The physical separation between the series diode and the common junction and the series and shunt diode is kept to the minimum Referring to Fig. 5, the driver circuit of the SP16T switch of the present invention is a fast driver circuit which provides a simultaneous switching waveform to all the switches The function of the driver is to serve as a voltage and current buffer between a command control signal source and a set of power supplies. The driver has been designed to deliver to each PIN diode either forward bias current (typically twenty five milliamps) or a reverse bias voltage (typically twelve volts), and to introduce minimum delay and with a capability of giving the required spike voltage and current to the diode, both, in the forward and reverse direction. Further, the driver has been designed for minimum video leakage. Video leakage refers to the spurious signals present at the RF output port of the switch when it is switched without an RF signal present The superior switching speed characteristics of the present SP16T switcn is realised mainly due to the simultaneous application of the switching voltages to the control ports of the SP2T and SP8T switches there by switching the SP16T switch in less than 25 nano seconds. Sequential switching of SP2T first and then SP8T switch is avoided in order to enhance the switching speed. The specification of the SP16T switch of the present invention is as follows. ACHIEVED SPECIFICATIONS (Table Removed) The present embodiment of the invention, which has been set for the above, was for the purpose of illustration and is not intended to limit the scope of the invention. It is to be understood that various changes, adaptations and modifications can be made in the invention described above by those skilled in the art without departing from the scope of the invention, which has been defined by following claims. WE CLAIM: 1 A single pole sixteen throw PIN diode (SP16T) switch for microwave applications having capability to switch the input to any one of the sixteen output ports and comprising: a cascading of one high power single pole double throw (SP2T) switch, two single pole eight throw (SP8T) switches and a driver circuit means; the said SP2T switch having silicon PIN diodes using all shunt configuration, the said SP8T switches utilising series shunt configuration, wherein the series devices are in the low-impedance (inducative) state and shunt devices are in the high impedance (capacitive) state. 2 A single pole sixteen throw PIN diode switch as claimed in claim 1 wherein said SP2T switch has three shunt diodes in each arm for getting the required isolation 3. A single pole sixteen throw PIN diode switch as claimed in claim 1 wherein said driver circuit means provides simultaneous switching waveform to all of the said SP2T and said SP8T switches, 4. A single pole sixteen throw PIN diode switch as claimed in claim 1 wherein said driver circuit means provides either the forward bias current or reverse bias voltage to each of the said PIN diodes. 5. A single pole sixteen throw PIN diode switch as claimed in claim 1 has a micro- strip line as the transmission medium. 6. A single pole sixteen throw PIN diode switch as claimed in claim 1 which operates in the entire microwave frequency range of 7.5 to 18 GHz with a capability of handling power up to + 33 db m. 7. A single pole sixteen throw PIN diode switch as claimed in claim 1 which has a switching speed of the order of 25 nano second. 8. A single pole sixteen throw PIN diode switch as claimed in claim 1 which has a resistance of about 100 ohms in dc return path of the said SP8T switch for improving the switching speed as will as power handling capacity. 9. A single pole sixteen throw PIN diode switch as claimed in claim 1 which requires only +5 volt and -15 volt for switching operation. 10. A single pole sixteen throw PIN diode switch substantially as described and illustrated herein.

Documents:

298-DEL-2003-Abstract-(22-12-2008).pdf

298-del-2003-abstract.pdf

298-del-2003-claims.pdf

298-DEL-2003-Correspondence-Others-(22-12-2008).pdf

298-del-2003-correspondence-others.pdf

298-del-2003-correspondence-po.pdf

298-del-2003-description (complete).pdf

298-del-2003-drawings.pdf

298-DEL-2003-Form-1-(22-12-2008).pdf

298-del-2003-form-1.pdf

298-del-2003-form-18.pdf

298-del-2003-form-2.pdf

298-DEL-2003-Form-3-(22-12-2008).pdf

298-del-2003-form-3.pdf

298-del-2003-gpa.pdf