GB2141298A - Single-pole multi-throw signal switch for modular audio-visual systems - Google Patents

Abstract

A video or rf switch includes a common port (538) and a plurality of second ports (A,B,C) to which the common port may be coupled by a plurality of switch sections in a single pole, multiple throw configuration. Each switch section includes a diode (514,522,612) coupled to the common port and a source of voltage (523,530,617) for energizing the diode. Conduction through the diode forward-biases it and causes current flow through a common biasing resistor (536). The voltage developed across the resistor back-biases the diodes of the other switch sections. A common blocking capacitor (516) keeps the back-bias voltage away from the common port. <IMAGE>

Description

SPECIFICATION Single-pole multi-throw signal switch for modular audio-visual systems This invention relates to a controllable switching arrangement for routing signals such as audio, video or radio-frequency television signals.

Modular audio-video systems including separate television tuners, video display monitors, signal processing units and the like have become available as separate freestanding components, joining video cassette recorders, video disc players and audio systems as modular entertainment components. Such components are often arranged into a system by interconnecting with cables. Interconnection by means of cables may not be appropriate in some instances, as for example in the case of a "cable-ready", television tuner which is adapted for receiving signals on channels allocated to both broadcast sources and CATV (cable) channels, where it may be desired to switch from a receiving antenna as a source, to a CATV outlet as a source. In this instance, a single-pole, double-throw equivalent switch would be appropriate for connecting the input of the tuner to one or the other of the sources.Some channels may be scrambled, whether on cable or broadcast, and a decoder may therefore be required for some channels but not for others. A fixed cabling of a decoder in the signal path of such a system is inappropriate, and the use of a switch may eliminate the need for disconnecting and reconnecting interconnection cables, depending upon the desired functions.

Manually operated signal switches are known for operation at video through UHF (ultra-high frequencies, generally considered as being 470 to 890 MHz for television purposes). However, manually operated switches are not well adapted for remote-control modes of operation. Electronically operated switches for operation with signals through the UHF television bands are also known. One type uses reed relays configured in coaxial or stripline arrangements and operated by electrically energized coils. While technically satisfactory, such relays with their drive circuits tend to be large and expensive, and furthermore are subject to reliability problems due to mechanical failure of the moving elements and anomalous failures thought to be due to the growth of metal dendrites in the vacuum or inert atmosphere of the relay at the low signal currents generally encountered.

Other electrically operated switches use switched diodes in arrangements in which a diode coupled in series with a low-level signal current path is either forward-biased by a control current to provide an ON function or reverse-biased by a reverse voltage for providing an OFF function. Such arrangements are effective, but the modulation of the forward ON control current by the signal current tends to change the dynamic impedance of the diode as a function of the signal, thereby introducing distortion, and at higher frequencies the capacitance of the diode in its OFF reverse-biased state tends to allow leakage of signal through the switch in the OFF state.The ON-state distortion modulation can be corrected by the use of a pair of "back-to-back" diodes series-coupled as to the signal current path, with both diodes forward-biased by a current in the ON mode, whereby a particular polarity of signal excursion causes oppositely-directed changes in impedance of the two diodes, so that the net change of impedance as a function of signal is reduced. The leakage problem in the diode-OFF state is ameliorated by the use of a pair of diodes, but since the reverse-bias capacitances will generally be of the same size, the reduction in leakage obtained by using two diodes is only 2:1, or 6dB.The through-loss or attenuation of a switch comprising a pair of diodes can be increased in the OFF-mode by the use of a third diode coupled to ground and to the junction between the first and second diodes, which third diode in the switch OFF state conducts to short any leakage signal to ground, thereby in the OFF-mode splitting the high impedance of the diode pair to formaT-configuration filter having improved attentuation characteristics.

U.S. Patent application Serial No. 437, 829, filed October 29, 1982, in the name of G. E. Theriault describes a radio4requency electronic switch including pairs of back-to-back diodes and shorting diodes as described above, and further including at the input of each of the multiple inputs or ports of a single-pole, multiple-throw radio-frequency switch' a further diode-controlled switch coupled to a matching resistor for terminating those ports which are decoupled from the common port. The common port requires no termination arrangement, since it is always coupled through an ON switch to a (presumably) matched load.

It has been noticed that switch arrangements including more than two throws (i.e., switch arrangements coupling a common port to one of a plurality of other ports where the plurality exceeds two)-tend to have poor impedance match and loss, especially at the higher frequencies. It is desirable to improve the match, reduce the loss and to do so without increase in cost.

In a single-pole multiple-throw electronic switch, multiple decoupling capacitors and bias components at and nearthe common point tend to degrade impedance match and introduce loss both by their physical presence which contributes shunt capacitance and resistive loss, and also because their physical presence causes the active switching element to be removed some distance from the common point. The multiple open switch elements are separated from the common point by open-circuited stub transmission lines less than one-quarter wavelength long, which therefore each present the common port with an effective capacitive reactance which further degrades the impedance match already degraded by the capacitance of the physical decoupling capacitors and the characteristics of the diode biasing components.The impedance of such stub transmission lines is a nonlinear function of their length, and it is imperative that the lengths be minimized.

In accordance with the invention, each electronic switch section of a single-pole, multiple-throw switch is arranged to be coupled to a common point to which a single biasing component is coupled and which can be coupled to an output conductor by a single blocking capacitor.

In the accompanying drawings: Figure 1 illustrates the general arrangment of a remotely controllable television signal switcher module coupled to a decoder, VCR and television receiver; Figure 2 is a schematic diagram of the signal-processing portions ofthe switcher module of Figure 1; Figure 3 is a schematic diagram of a broadband signal amplifier suitable for use in the arrangement of Figure 2; Figure 4 is a schematic diagram of a hybrid signal splitter adapted for use in the arrangement of Figure 2; Figure 5 is a schematic diagram of an embodiment of the invention including switch drive circuitry; Figure 6 is a schematic diagram of a single-poIe, triple-throw embodiment of the invention; Figure 7 is a schematic diagram of a single-pole, quadruple-throw embodiment of the invention;; Figure 8 is a double-size plan view of a portion of a printed-circuit board suitable for use with the embodiment of Figure 7;and Figure 9 illustrates an embodiment without an impedance matching section.

In Figure 1, a switcher module 10 receives signal inputs at input terminals 12, 14 and 16 from sources of video signal such as cable A, cable B and an auxiliary source which may be from an antenna, video disc player orvideocassette recorder (VCR). Signals are routed from these sources and from a DECODER input terminal 18 to a TV terminal 20, VCR output terminal 22 andor a decoderoutputterminal 24, under the control of a receiver and controller 26, which may physically be a portion ofswitcher 10.Receiver and controller 26 receives control signals from a remote 28 in known fashion which signals are used to control the state of switches within module 10 to direct the selected signals to television display 30 and to the VCR 32, and to interpose decoder 34 in the signal path as required for decoding scrambled signals. Controller 26 may include memory and a microcomputer as required to remember, for example, which selected channels are scrambled and to automatically interpose descrambler 34 in the signal path when a scrambled signal is selected for viewing.

Figure 2 is a general schematic diagram of the signal flow path portions of switch module 10.

Corresponding input and output p-orts are designated by the same reference numbers as in Figure 1.

Generally, a single-pole, double-throw equivalent switch 210 is associated with decoder output terminal 24, a single-pole triple-throw switch 212 is associated with VCR output terminal 22 and a single-pole quadruple-throw switch 214 is associated with the TV output terminal.The output terminals are illustrated as being coaxial, corresponding to the requirements for video or radio-frequency signal operation, but it will be understood that equivalent transmission lines can be used, and in particular strip line or micro-strip conductors may be used to-interconnectthe input terminals and theoutputtermina[s. In Figure 2,the signals on cable A are coupled by way of input terminal 12 to a broadband amplifier designated as 300, the output of which is coupled to a -3dB hybrid splitter 216 which splits the signal amplitude into a first portion conducted over a conductor 218 to an input terminal 228 of switch 210 and a second portion directed along-a conductor 220 to a second -3dB hybrid splitter 222.Similarily, the signal applied to terminal 14 from cable B is amplified by302 and split into two equal portions by splitter 224. One of the portions is directed to a second input terminal 226 of switch 210 and a second portion is directed to splitter 228 where the signal amplitude-is again divided. Thus, a portion of the signal applied to cable A and cable B is simultaneously available at inputs of each of switches 210,212 and and 214.

Switch 210 is arranged to selectoneorthe other of the signals applied to its input and couple itto decoder terminal 24. The decoded signal from the decoder (not shown in Figure 2) is applied to decoder input terminal 18 and to a signal splitter 230, outputs of which are coupled to input terminals of switches 212 and 214. Thus, switch 212 has available for coupling to VCR output terminal 22 signals from cables A or B or from the decoder. As mentioned previously, an auxiliary television signal source may be coupled to auxiliary input 16, thereby making one of the signals from cables A or B, from the decoder or from the auxiliary input available to TV output 20 by operation of switch 214.While switches 210, 212 and 214 are illustrated as being composed of multiple single-pole single-throw switches, these are arranged and operated so-as to be equivalent to single-pole, multiple-throw switches.

Figure 3 illustrates a broadband amplifier suitable for use through the television VHF and UHF bands. In Figure 3, amplifier 300 includes a transistor 302 having its base coupled to a source of RF signals by a capacitor 304 and its collector coupled to a RF output port by a capacitor 306. Collector voltage is applied to the collector of transistor 302 from a source (B+) of voltage by a pi-filter designated generally as 308 and by RFC (radio frequency choke) 310. Bias for the baste of transistor 302 is provided by a voltage divider including resistors 312,314 and and 316 coupled between the collector and ground. Collector current is controlled principally by a resistor 318 connected in series with a small-value resistor 320 between the emitter of the transistor and ground. The output impedance of amplifier 300 is reduced to approximately 75 ohms, the characteristic impedance of the system, by unbypassed-shunt feedback resistor 314. The input impedance is controlled by resistor 320 which is bypassed to ground by a pair of capacitors 322 and 324.

Figure 4 illustrates in schematic form the well-known 3db hybrid-splitter including a center-tapped ferrite-core transformer 410, one -end of which is coupled to each output ports. A 150 ohm resistor is bridged across the arms of the transformer to control the impedance in case one of the output ports is unterminated.

The impedance seen looking into the centertap of transformer 410 with the output ports terminated is one-half of the 75 ohm output impedance or 37.5 ohms. Step-down input transformer 412 matches the 75 ohm input source impedance to the 37.5 ohm impedance of the transformer tap. Because of the low impedance of connecting conductor 414, a capacitor 416 is connected to the center of the conductor to form a low-pass filter having a cut-off frequency above the frequency of interest.

Figure 5 illustrates in schematic form single-pole double-throw switch 210 and its ancillary control circuits.

In Figure 5, the multiple output ports (two in number) are designated 226 and 228, corresponding to the designations in Figure 2. Port 228 (which may be coaxial or micro-strip equivalent as mentioned previously) is coupled to A-B switched RF output port 24 by way of switch section A including a dc blocking capacitor 510, back-to-back diodes 512 and 514, and common blocking capacitor 516. Port 226 is coupled to A-B switched RF output port 24 by way of common capacitor 516 and switch section B including blocking capacitor 518 and back-to-back diodes 520 and 522. Control voltages are applied to sections A and B containing series switch diodes 512, 514 or 520, 522 by way of RFC 524, 526, respectively from switch driver circuits designated generally as 528, 530 respectively.Each switch section is rendered conductive when its switch driver applies +12 volts to the junctions 545 or 550 between diode pairs, by way of the corresponding RF choke. Only one switch section or diode pair is allowed to be conductive at any time, as suggested by switch waveforms 532, 534 illustrated in the Figure.

When switch driver 528 is energized to provide +12 volts applied by way of RFC 524 to the common anodes of diodes 512 and 514, current flows through conductive diode 514 and through a resistor 536 coupled to common point 538. Current also flows through conductive diode 512 and through a resistor 540 coupled between node 544 at the cathode of diode 512 and ground. With switch driver 528 producing +12 volts on the conductor 542, common point 538 and node 544 are maintained at a voltage of one Vbe below 12 volts. The voltages at nodes 544 and 545 maintain diodes 546 and 549 back biased and therefore essentially out of the circuit. Under this condition, diodes 512 and 514 have a relatively low impedance and couple port 228 to port 24.

As mentioned, only one switch section is maintained ON at any one time. The remaining switch sections are maintained OFF by grounding the common point between the diodes. In Figure 5 switch driver 530 maintains a ground potential on the conductor 548 during those times in which switch driver 528 maintains +12 volt on conductor 542. With conductor 548 and therefore node 550 at ground, diode 522 is back biased by the voltage generated across resistor 536 due to conduction of diode 514. With node 550 at ground, current flows from the +5V supply through resistor 556 and diode 552, thereby rendering diode 552 conductive and coupling grounded capacitor 558 to node 550. Conduction from the +5V supply through 75 ohm matching resistor 560, diode 554 and resistor 562 to ground places a substantial positive voltage across resistor 562 which back-biases diode 520.In this condition, diodes 520 and 522 are a HIGH impedance and diode 552 couples a low impedance to junction 550 therebetween, thereby forming switch section B into a high-attenuation T-filter which reduces leakage through the switch section. Conduction of diode 554 couples matching resistor 560 across the input of port 226 to maintain an impedance match at the port when switch section B is OFF thereby preventing reflections which may cause ghosts and also preventing reflections which may cause ghosts and also preventing a voltage rise which might increase coupling through the switch section.

Switch drivers 528 and 530 are similar, so only switch driver 528 will be described in detajl. Switch driver 528 includes a transistor 570 having its emitter coupled to ground and its collector coupled to +12 volts by way of a resistor 572. A second transistor 574 has its base coupled to the collector of transistor 570 and its collector coupled to the +12 volt bus. The output from switch driver 528 is taken from the emitter of transistor 574. A diode 576 having its anode coupled to the emitter of transistor 574 and its cathode coupled to the transistor 570 allows flow of current in conductor 542 when the switch driver is in the grounding mode.

It should be noted that switch driver 528 is inverting, in that zero input volts (logic LOW input) produces +12 output volts, and a logic one or HIGH input signal applied to the base of transistor 570 results in a zero volt or grounded output condition on conductor 542. The mode of operation of switch 210 is under the control of logic signals applied to a conductor 580 applied directly over a conductor 582 to the input of switch driver 530 and applied by means of an inverting amplifier 584 to the input of switch driver 528. As suggested by waveform 586 illustrated as being applied to logic control 580, switch section A is conductive when conductor 580 is HIGH (and therefore switch section B is nonconductive), and switch section B is conductive when conductor 580 is LOW (and therefore switch section A is nonconductive).

Figure 6 illustrates a single-pole triple-throw switch which corresponds with switch 212 illustrated in Figure 2 and generally corresponding in form to switch 210 of Figure 5 but including a further switch section C including switch diodes 612,614 coupled to common point 538 and by way of a coupling capacitor 616 to a C port 610. The A, B and C ports illustrated in Figure 6 are for coupling to outputs of splitters 222, 228 and 230 in Figure 2. A switch driver designated generally as 617 applies switch drive signals over a conductor 618 and through a RFC 620 to node 622 at the junction of diodes 612 and 614. Other diodes and components of switch section C of Figure 6 have reference numbers corresponding to the reference numbers of components switch section A of Figure 5 but in the 600 series rather than the 500 series. It should be noted that resistor 536 and capacitor 516 in Figure 6 are common to switch sections A, B and C. Thus, the cathodes of diodes 514,522 and 612 can be physically close to common point 538, thereby reducing the physical length of stub line remaining when the switch sections are OFF. The stub conductor length is illustrated in Figure 6 as 650, 652, and 654.

Switch drivers 528 and 530 receive control signals over conductors 581,582 and 656 from logic circuitry designated generally as 658. The logic circuits receive positive-logic input signals on MSB conductor 668 and LSB conductor 666. In order for the A section of the switch to be conductive, conductor 581 must be LOW and conductors 582 and 656 must be HIGH. The LOW on conductor 581 is accomplished by OR gate 670 which receives input signal 0,0 on conductors 666 and 668 to produce a LOW output on conductor 581, while inverters 672 and 674 produce a logic HIGH on conductors 582 and 656.Similarly, conduction of switch section B is accomplished by placing a logic LOW on conductor 582 and logic HIGH on conductor 581 and 656, which is accomplished by means of an OR gate 676 and inverter 672 for producing the logic low on conductor 582, while OR 670 and inverter 674 produce logic HIGH on conductors 581 and 656. Conduction of switch section C is established by a MSB of one which is inverted by inverter 674 to enable switch driver 616, while a HIGH is coupled through OR-gates 670 and 676 to place switch sections A and B is the OFF state.

Figure 7 illustrates a single-pole quadruple-throw switch which is similar to switch 600 of Figure 6 but further includes a switch section D and-further output port. The switch drivers are not illustrated in schematic detail. The logic circuits are designated generally as 700 and produce appropriate switch driver control signals according to the table in Figure 7. It will be noted that four diodes have their cathodes adjacent common port 538 and have resistor 536 in common. It will be recognized that no matter how many throws a switch assembly may have, only one bias resistor 536 and output capacitor 516 are necessary. Consequently, the diodes may be placed as close to common port 538 as their physical size allows and provides the advantages of the invention.

Figure 8 is a plan view of that portion of the arrangement of Figure 7 carrying switched signals. In Figure 8, the shaded regions represent conductors on the component side of a 1/32 inch (0.08 mm) double-sided G-1 0 glass-epoxy board. The underside of the board (not shown) is completely covered with conductors except at those points at which a component lead protrudes from the side illustrated. The elements in Figure 8 are designated with the reference numbers used in Figure 7 for ease of identification.

In a particular embodiment of the invention, the following component values were found to be effective: Diodes Toshiba 1 3V99 Capacitors 0.01 a1F chip Coils- 2.2 FH axial-lead plastic molded resistors Resistor 547 75 Ohm* Resistor 560 75 Ohm* Resistor 647 75-Ohm* Resistor 747 75 Ohm* Resistor 540 1K Ohm Resistor 555 1K Ohm Resistor 556 1K Ohm Resistor 562 1K Ohm Resistor 640 1K Ohm Resistor 655 1K Ohm Resistor 740 1K Ohm Resistor 755 1K Ohm *(equal to characteristic Z) Other embodiments of the invention will be apparent to those skilled in the art. In particular, as in Figure 9, a biasing means in the form of a radio-frequency choke or inductor may be substituted for the matching diode arrangement. Also, the common biasing resistor (536) may be coupled to the +5 volt supply.

Claims (9)

1. A single-pole multiple-throw electronic switch for coupling a common port to one of first plurality of second ports, comprising: a plurality of signal switch sections equal in number to said first plurality, each of said signal switch sections comprising first and second diodes having like diode terminals coupled together at a first junction and connected in series for the flow of signal therethrough, each of said diode pairs having a terminal of said second diode remote from said first junction ac-coupled to one of said plurality of second ports; a plurality of third diodes equal in number to said first plurality, each of said third diodes having a terminal coupled to one of said first junctions, that terminal of said third diode coupled to said first junction being dissimilar to those terminals of said first and second diodes coupled to said first junction;; a point of first potential relative to a reference potential; a plurality offirst resistance means equal in number to said first plurality, each of said first resistance means being coupled to a terminal of one of said third diodes and to said point of first potential; a plurality, equal to said first plurality, of low-impedance means, each coupled to that terminal of one of said third diodes remote from said first junction and to a point of reference potential for bypassing to said point of reference potential any signal appearing at said first junction when the corresponding third diode is conducting;; a plurality of fourth diodes equal in number to said first plurality, each of said fourth diodes having a terminal coupled to one of said terminals of said second diode remote from said first junction to form a second junction, said coupled terminals of said second and fourth diodes being like; a plurality of second resistance means equal in number to said first plurality, each of said second resistance means being coupled to a point of potential and to that terminal of said fourth diode remote from said second junction; each of said second resistance means having a resistance substantially equal to the design characteristic impedance of the system for presenting to the corresponding second port a matching impedance when the corresponding first and second diodes pre nonconducting and the corresponding fourth diode is conducting; a plurality equal in number to said first plurality of third resistance means, each of said third resistance means being coupled to one of said second junctions and to a point of reference potential for providing a path for the flow of bias current through at least each of said fourth diodes; a second source of potential greater than said first potential;; first controllable dc switch means coupled to said second source of potential, to said point of reference potential and to said first junctions for coupling to one of said first plurality of first junctions a potential greater than that of said first potential and poled so as to reverse-bias the corresponding third and fourth diodes and forward-bias the corresponding second diodes associated with said one of said first plurality of junctions for allowing signal flow between the corresponding second port to said one first junction;; fourth resistance means direct-coupled to each of the terminals of said first diodes remote from first junctions and to a point of reference potential for providing a path for the flow of current through that first diode coupled to that one first junction to which said first controllable switching means couples said potential greater than that of said first potential, whereby a bias voltage appears across said fourth resistance means; dc blocking means coupled to said common port and to said fourth resistance means for preventing said bias voltage from appearing at said common port;; second controllable dc switching means coupled to each of said first junctions for applying a reference potential to each of said first junctions other than said one of said first plurality of first junctions for reverse-biasing said second diodes associated with said first junctions other than said one first junction whereby said bias voltage reverse-biases said first diodes coupled to said first junctions other than said one first junction for improving the isolation of said common port from said plurality of second ports other than said corresponding one; and control means coupled to said first and second controllable dc switching means for operating said first and second controllable dc switching means simultaneously for allowing signal flow through a selected one of said signal switch sections when said first controllable dc switching means applies said greater potential to said first junction of said selected signal switch section and for blocking the remainder of said plurality of signal switch sections when said first junctions of said remainder of signal switches are coupled to reference potential by said second controllable dc switching means.

2. An electronic switch according to Claim 1 wherein said first and second dc switching means comprise isolation means for preventing signal from reaching the potential sources.

3. An electronic switch according to Claim 2 wherein said isolation means comprises a choke.

4. An electronic switch according to Claim 1 wherein said point of potential to which said second resistance means is coupled is said point of first potential, and wherein said point of first potential is at said reference potential at signal frequencies.

5. An electronic switch according to Claim 1 wherein said junctions of said first diodes remote from said first junction are physically closely spaced for reducing the length of stub-transmission lines coupled to said common port.

6. A single-pole multiple-throw electronic switch for coupling a common port to one of first plurality of second ports, comprising: a plurality ofsignal switch sections equal in number to said first plurality, each of said signal switch sections comprising first and second diodes having like diode terminals coupled together at a first junction and connected in series for the flow of signal therethrough, each of said diode pairs having a terminal of said second diode remote from said first junction ac-coupled to one of said plurality of second ports;; a plurality of third diodes equal in number to said first plurality, each of said third diodes having a terminal coupled to one of said first junctions, that terminal of said third diode coupled to said first junction being dissimilar to those terminals of said first and second diodes coupled to said first junction; a point of first potential relative to a reference potential; a plurality of first resistance means equal in number to said first plurality, each of said first resistance means being coupled to a terminal of one of said third diodes and to said point of first potential; ; a plurality, equal to said first plurality, of low-impedance means, each coupled to that terminal of one of said diodes third remote from said first junction and to a point of reference potential for bypassing to said point of reference potential any signal appearing at said first junction when the corresponding third diode is conducting; a plurality of biasing means equal in number to said first plurality, each of said biasing means having a terminal coupled to one of said terminals of said second diodes remote from said first junction to form a second junction, and also having a terminal coupled to a point of potential;; a plurality, equal in number to said first plurality, of second resistance means, each of said second resistance means being coupled to one of said second junctions and to a point of reference potential for providing a path for the flow of bias current through at least said biasing means; a second source of potential greater than said first potential; first controllable dc switch means coupled to said second source of potential, to said point of reference potential and to said first junctions for coupling to one of said first plurality of first junctions a potential greater than that of said first potential and poled so as to reverse-bias the corresponding third diode and forward-bias the corresponding second diode for allowing signal flow between the corresponding second port and said one first junction;; third resistance means direct-coupled to each of the terminals of said first diodes remote from said first junctions and coupled to a point of reference potential for providing a path for the flow of current through that first diode coupled to that one first junction to which said first controllable switching means couples said potential greater than that of said first potential, whereby a bias voltage appears across said third resistance means; common dc blocking means coupled to said common port and to said-third resistance means for preventing said bias voltage from appearing at said common port;; second controllable dc switching means coupled to each of said first junctions, other than to said one of said first plurality of first junctions to which potential is applied by said first controllable switch means for applying a reference potential to each of said firstjunctions, other than said one,for reverse-biasing said second diodes whereby said bias voltage reverse-biases said first diodes coupled to said other first junctions for improving the isolation of said common portfrom said plurality of.second ports other than said corresponding one; and control means coupled to said first and second controllable de switching means for operating said first and second controllable de switching means simultaneously for allowing signal flow through a selected one of said signal switch sections when said first controllable de switching means applies said greater potential to said first junction of said selected signal switch section and for blocking the remainder of said plurality of signal switch sections when said first junctions of said remainder of signal switches are coupled to reference potential by said second controllable de switching means.

7. An electronic switch according to Claim 6 wherein said controllable switching means comprises inductance means.

8. An electronic switch according to Claim 6 wherein said biasing means comprises resistance means.

9. An electronic switching arrangement substantially as hereinbefore described with reference to Figures 5,6,7,8 or 9 of the accompanying drawings.