WIDEBAND SWITCHING ARCHITECTURE

Abstract: A method and apparatus for switching signals through a network with minimal crosstalk. Each stage (202-204) of the network has a plurality of switching input (303-305) and output (300-302) arrays. Each input array has one input and each output array has one output. Outputs and inputs of the respective input and output arrays, are interconnected to form a nonblocking stage. Each array is a single integrated circuit. Crosstalk is reduced by allowing only one signal to be present in an array at any one time and by grounding all unused outputs and inputs.

Description: WIDEBAND SWITCHING ARCHITECTURE Technical Field This invention relates to a method and apparatus for switching wideband signals and, in particular, for reducing crosstalk within the switching network. Background of the Invention The high frequencies required for wideband digital transmission, may create crosstalk problems within a switching network. In particular, when a space division switching network contains a semiconductor crosspoint array, the crosstalk problems are acute at high frequencies. There are two main contributors to such crosstalk problems. One is the leakage between the conductors and substrate caused by the relatively poor insulating qualities of the substrate and the capacitive effect among signals in close proximity within the semiconductor array. The second factor is the OFF state capacitive coupling between the input and output of the crosspoint*s switching transistors. At higher frequencies, this capacitance declines resulting in increased crosstalk. As a signal is switched through a multistage telephone-type network, these factors result in a cumulative, linear increase in crosstalk, the total being equal to the sum of the crosstalk for each stage of the network. The approach taken by the prior art to eliminate this crosstalk problem has been to reduce the OFF state capacitance of the crosspoint, to increase the dielectric isolation of the substrate and to physically distribute the conductors within the semiconductor array in a manner so as to reduce the capacitive coupling between conductors. These techniques have required larger semiconductor chips, and hence, lower yields and higher costs. In view of the foregoing, there exists a need for a switching network architecture which can utilize semiconductor arrays which are easy to manufacture and meet the necessary crosstalk requirements. Summary of the invention The foregoing problems are solved by connecting a plurality of wideband signal sources to a plurality of wideband receivers via a multistage network which is controlled by a switch controller. Each network stage comprises a plurality of switching elements with each switching element having a plurality of input and output switching arrays. Within a switching element, each input switching array has an output terminal connected to an input terminal of every output switching array. Each switching array is one semiconductor part; each input switching array has only one input terminal for receiving a wideband signal, and each output switching array has only one output terminal for transmitting a wideband signal. By reducing the number of external wideband signal connections to one per semiconductor part, crosstalk is reduced. Each input switching array has a pair of crosspoint devices associated with each output terminal. One crosspoint device is capable of connecting the associated output terminal to the input terminal, and the other crosspoint device is capable of connecting the associated output terminal illustratively to ground. The switch controller controls the crosspoint devices so that one output terminal is connected to the input terminal receiving the desired signal and the remaining output terminals are connected to ground, thus reducing the effect of crosstalk within the switching input array by providing a low impedance path to ground for any undesired signals. Similarly, each output switching array has a pair of crosspoint devices associated with each input terminal. One crosspoint device is capable of connecting the associated input terminal to the output terminal and the other crosspoint device is capable of connecting the associated input terminal to ground. The switch controller controls the crosspoint devices so as to connect the input τ CMPI terminal receiving the desired signal to the output terminal and the remaining input terminals to ground which reduces crosstalk. If no wideband signal is to be transmitted via a particular switching output array, crosstalk is further reduced by connecting the output terminal to an input terminal of the switching output array which is being grounded by a crosspoint device in an input switching array via the associated output terminal of that input switching array. The novel method served to transmit wideband signals from a wideband signal source to a wideband signal receiver. The steps involve communicating the wideband signal from the wideband signal source through an input array and transferring the signal from an output terminal of the input array through an output array to the wideband signal receiver while controlling all other terminals in the various arrays to known states to reduce crosstalk. The remaining terminals within the switching network are held to known states by the steps of connecting all other input and output terminals in the active output and input arrays, respectively, to ground, connecting all output terminals of all other input arrays to ground, connecting output terminals of other unused output terminals to ground via a connection to the active input array and connecting all other input terminals of the inactive output arrays to ground. Brief Description of the Drawing FIG. 1 shows in block diagram form, a communication switching system utilizing a voiceband switch for the switching of telephone conversations and a video band switch for the switching of video information, in accordance with the present invention; FIG. 2, in block diagram, shows the network modules and control which comprise the video switch of FIG. 1; OV.?I_ FIG. 3 shows in greater detail the internal structure of a switching element shown in FIG. 2; FIG. 4, in block diagram form, shows the details of the switching arrays of FIG. 3. Detailed Description FIG. 1 shows a communication system which is capable of switching both voice and video information. Telephone switching office 100 consists of switching processor 104 which performs the necessary control functions to switch voice information by establishing paths through voice switch 103. In addition, switching processor 104 provides access to the video vendors 106, 107 for customers 101, 102 by establishing paths through video switch 105. The types of video services provided by video vendors 106, 107 include movies, catalog service, reference information and travel information. As noted in fig. 2, video switch -105 consists of video switch controller 201 and three network stages 202 through 204. Controller 201 receives commands from switching processor 104 directing the establishment of paths through the network. Network stage 202 contains 16 modules, illustrated by modules 210 and 211. Network stage 203 contains 31 modules, illustrated by modules 212 and 213. Network stage 204 contains 64 modules illustrated by modules 214 and 215. Network stage 202 receives signals from 256 video vendors, including vendors 106 and 107. The internal structure of the modules which comprise network stage 202 is illustrated by module 210 which receives signals from 16 video vendors via 16 input conductors 218 through 220. Module 210 has 31 output conductors 244 through 247 and two switching elements 216 and 217. Each module of stage 202 is connected to each of the modules which comprise network stage 203. For example, output conductor 244 from switching element 216 of module 210 is connected to module 212, and output conductor 247 from element 217 of module 210 is connected to module 213. This interconnection allows any module in stage 202 to set up a path to any module in stage 203. Network stage 203 contains 31 modules, such as module -212. Module 212 is comprised of four switching elements 224 through 227, each of which is connected to one of the output conductors from each module of network stage 202. Module 212 has 64 output conductors, each of which connects to a different one of the 64 modules in network stage 204. For example, output conductor 228 connects to module 214 and output conductor 229 connects to module 215. Module 214 has two switching elements 232 and 233, and has 31 inputs and 16 outputs. Module 214 has one input connected to each of the 31 modules which comprise network stage 203 and one output connected to each customer, such as customer 101 connected via output conductor 234. The operation of video switch 105 is illustrated by video vendor 106 transmitting to customers 101 and 102. Switching processor 104 via video switch controller 201 sets up the necessary connections by transmitting control signals via cables 240, 239, 238, 241, 242 and 243. Thus switching element 216 transmits the signals from vendor 106 via input conductor 218 to switching element 224 via conductor 244 and via output conductor 228, and switching element 232 to customer 101 via output conductor 234. Video vendor 106 transfers information to customer 102 through the following path: conductor 218, module 216, conductor 244, switching element 227 of module 212 to conductor 229 for transmission to module 215. Module 215 takes the information being transmitted via conductor 229 and transmits this information to customer 102 via conductor 237. A detailed block diagram of switching element 216 is shown in FIG. 3. The other switching elements are similar in construction. Switching element 216 consists of array selector 308 and 32 arrays, e.g., 300 through 305. O Arrays 300 through 302 are output arrays, with only one output, and arrays 303 through 305 are input arrays with only one input. Each array consists of one integrated circuit. The outputs and inputs for input and output arrays, respectively, are connected to ground if not being used to transfer a signal. These techniques reduce crosstalk by reducing the number of crosstalk sources and by providing low impedance paths to ground for spurious signals. Array selector 308 decodes the address signals being transmitted via address bus 307 in cable 240 from video switch controller 201. The decoded information is used to determine which array is to store the information transmitted via data bus 306 in cable 240. Array selector 308 decodes the information transmitted via address bus 307 and transmits a "1" on conductors 310 through 314 to the array which is to store the information being transmitted via data bus 306. For example, array 303 responds to the transmission of a "l" via conductor 309 from array selector 308 by storing the information being transmitted via data bus 306 in the 32 crosspoints of array 303. The crosspoints are grouped as pairs. For example, crosspoints 315, 320 comprise one pair r 316, 319 a second pair and 317, 318 a third pair. With respect to each pair of crosspoints, one of the crosspoints is ON while the other is OFF. Within array 303, crosspoint 315 is either connecting conductor 218 to conductor 321 or crosspoint 320 is connecting conductor 321 to ground. Crosspoint pair 316 and 319 and crosspoint pair 317 and 318 function in the same manner, with respect to conductors 322 and 323. As an example of how switching element 216 functions in connecting the 16 input conductors 218 through 220 to the 16 output conductors 244 through 246, consider the manner in which the arrays would have to be set up by the video switch controller 201 via the array selector 308 and the control section of arrays 300 through 305 to connect input connector 218 to output connector 245. Within array 303, crosspoint 316 would be turned ON connecting conductor 218 to conductor 322; and within array 301, crosspoint 326 would be ON connecting conductor 322 to output conductor 245. Also, within array 303, all of the crosspoints 318 through 320, except crosspoint 319, are ON connecting the 15 conductors 321 through 323 to ground except for conductor 322. For example, crosspoint 320 is ON, thus, connecting conductor 321 to ground. Similarly, within array 300, crosspoint 325 is ON also connecting conductor 321 to ground, and this is true of all of the 15 arrays 300 through 302 except array 301. All of these arrays would connect the conductor from array 303 to ground. Array 301 would ground all other input conductors. A second example is where input conductor 218 is to be simultaneously connected to' output conductors 244, 245 and 246. Within array 303, input conductor 218 is connected to conductors 321, 322 and 323 by turning ON crosspoints 315, 316 and 317. Within array 300, crosspoint 324 is turned ON connecting conductor 321 to output conductor 244; in array 301, crosspoint 326 is turned ON connecting conductor 322 to output conductor 245; and in array 302, crosspoint 328 connecting conductor 323 to output conductor 246. In this example, all other output conductors from array 303 are connected to ground via crosspoints 318 through 320, with the exception of crosspoints 318, 319 and 320. In addition, the conductors connected to ground within array 303 are connected to ground also in the output arrays, with the exception of arrays 300, 301 and 302. In addition, if no signal is being transmitted through an output array, the output conductor of the array is connected to a grounded conductor from an input array. For the first example given above and assuming no signal being transmitted on output conductor 244, video switch controller 201 turns crosspoint 324 ON which connects conductor 244 to ground via conductor 321, and crosspoint 320. The input crosspoints 330 and 331 are turned ON and output crosspoints 332 through 333 are turned OFF. The result is that output conductor 244 is connected to ground which reduces crosstalk being coupled into conductor 244. From the foregoing description of switching element 216 which is illustrative of all the switching elements in video switch 105 and the examples relating to that description, each of the input arrays 303 through 305 has only one input conductor over which the video signal is transmitted. .This means that there can be no crosstalk within any array between video signals, since, only one video signal is present in the array. Also, each output array 300 through 302 only has one output conductor for transmission of a video signal. Each array, regardless of whether it is an output or an input array, has only one video signal being transmitted through it at any point in time, and all other conductors, except for the conductors being used to transmit the video signal are grounded. This grounding of all unused conductors provides a low impedance path for any potential crosstalk sources. Each switching element achieves a two-crosspoint isolation effect, since the video signal is transmitted through a crosspoint in an input array and a crosspoint in an output array. A detailed block diagram is shown of array 303 of FIG. 3 in FIG. 4, and is illustrative of all of the various arrays within video switch 105. The crosspoints 315 through 320 are bilateral switches which are capable of transmitting the video signal from the I terminal to the 0 terminal, or vice versa. A crosspoint is turned ON and will conduct the signal from either the I to the 0 terminal, or vice versa, when a "1" is present at the C input terminal. The crosspoints are controlled by the content of latches 401. The video switch controller 201 of FIG. 2 writes information into latches 401 by transmitting 16 bits on data bus 306 which is part of cable 240 and by transmitting address bits on address bus 307 which is also part of cable 240. Array selector 308 decodes the address bits being transmitted via address bus 307 and transmits a "1" on conductor 309 if the data is to be stored in latches 401. Latches 401 respond to the "1" being transmitted via conductor 309 to store the 16 bits being transmitted via data bus 306. Each crosspoint pair, such as, 315 and 320 has associated with it, one bit in latches 401 which is used to control the state of the particular crosspoint pair. For example, the state of the bit associated with crosspoint pair 315 and 320 is transmitted via conductor 402. If a "1" is being transmitted via conductor 402, then crosspoint 315 is turned ON since there is a "1" present at its C input and crosspoint 320 is turned OFF. Crosspoint 320 is turned OFF since inverter 403 inverts the "1" being transmitted via conductor 402 and transmits a "0" via conductor 404 to the C input of crosspoint 320. The other crosspoint pairs function in a similar manner. O FI

Claims: Claims 1. A wideband switching system comprising a multistage switching network (105) , each stage (202-204) having a plurality of switching elements (216, 217, 224-227, 232, 233); and a switching controller (201); CHARACTERIZED IN THAT each switching element (e.g. 216) comprises a plurality of input switching arrays (303-305) with one input and a plurality of outputs and a plurality of output switching arrays (300-302) with one output and a plurality of inputs; each output of one of the input switching arrays is connected to an input of a different one of the output switching arrays; each input of the input switching arrays of a first stage (202) is connected to a different signal source (106, 107); each output of the output switching arrays of the first stage is connected to different input switching arrays of the second stage (203); and each output (228, 230, 231) of the.output switching arrays of the second stage is connected to a different signal receiver (101, 102). 2. A wideband switching system in accordance with claim 1 CHARACTERIZED IN THAT each input array (303-305) comprises first switch means (315-317) responsive to a signal from the controller (201) for connecting a selected one of the array outputs (321, 322, 323) to the array input (218); and second switch means (318-320) responsive to the signal from the controller for connecting the remaining outputs to ground. 3. A wideband switching system in accordance with claim 1 CHARACTERIZED IN THAT each output array (e.g. 300) comprises first switch means (324, 332, 333) responsive to a signal from .J - li ¬ the controller (201) for connecting a selected one of the array inputs (e.g. 321) to the array output (244); and second switch means (325, 330, 331) responsive t the signal from the controller for connecting the remainin input . to ground.

Inventors: TERASLINNA KARI TAPIO, TERASLINNA, KARI, TAPIO
Applicants: WESTERN ELECTRIC CO, WESTERN ELECTRIC COMPANY, INC.
Application year: 1982
Main classification: H04N7
IPC codes: H04M3, H04Q3