FR2721155A1 - HF single-pole throw switch e.g. for switching satellite signals to receiver - Google Patents

Abstract

The switch includes a number of input ports and the same number of switches. An input matching circuit (31,32) is connected to one of the input ports. The input electrode of a transistor (BJT1,BJT2) is connected to the matching network output (36). A junction (J) connects together all the outputs of the transistors in the switches and an output matching circuit is coupled to the junction. A DC voltage biasing network (35) provides bias voltages for respective transistors. On switching a certain input signal, only one transistor operates in the linear region with the rest operating in cut-off. The transistors are arranged in common-emitter mode. A number of active push-down elements push the base voltages of the transistors below forward operating bias voltages to force the transistors to operate in the cut-off region. Each push-down element is connected to the DC insertion point of the base of either transistor.

Description

Multi-directional single pole high frequency switch operating

with gain

  The present invention relates to a high frequency switch

  unipolar quence with several directions operating with gain, and in particular the circuit of a high frequency switch

  unipolar with several directions made up of transistors.

  The switch of the present invention is particularly suitable

  especially good for switching satellite signals to polar-

  vertical and horizontal position. The switching elements currently used to switch or select high frequency signals are relays or PIN diodes. However, in the case where a relay is used as a selector switch, since the relay is a mechanical element, it has a higher failure rate and a shorter service life, compared to electronic elements, when the temperature is too high or too low. Furthermore, since a relay is a passive element, it cannot provide any gain to the signals. Using a PIN diode as a selector switch can solve the problems of high failure rate and short service life posed by the use of a relay. Unfortunately, it requires more elements to achieve the same degree of signal separation (4 to 8

  PIN diodes are usually necessary to obtain a separation

  ration by attenuation of 20 dB in UHF for switching

  ). In addition, this type of circuit generally introduces losses in signal transmission and, therefore, does not

cannot provide gain.

  The object of the present invention is to provide a reliable and long-life selection switching circuit having

  fewer elements, a simple circuit structure and a function-

  gain control, which uses transistors as switching elements. The selection of the signals is controlled by switching the bias voltages in operation of the transistors to operate the transistors in the linear domain (conductive transistor, or "unblocked") in the

  breaking range (non-conductive, or "blocked" transistor).

  The invention also uses a particular arrangement for the impedance matching network which is necessary for

  the input and output of the transistors to be connected in such a way

  so that the structure of the switching circuit becomes more

  simple and that the design of this type of circuit is easier

  eyelash. Furthermore, since the transistors used are inexpensive elements operating with a gain, it is not necessary to provide additional amplifiers to compensate for the signal losses in the circuit of the present invention. Therefore, the cost of the circuit may be still

more reduced.

  These objects, features and advantages of the invention are

  will be better understood and appreciated on reading the description

  of preferred embodiments given below in relation to the appended drawings, in which:

  - Figure 1 is a block diagram of a circuit which uses

  reads bipolar transistors as amplification elements;

  - Figure 2 is a partially block diagram of a pre-

  mier embodiment of the multi-directional unipolar switching circuit according to the invention; - Figure 3 is an equivalent diagram of the circuit shown in Figure 2; - Figure 4 is a block diagram of a second embodiment of a multi-directional unipolar switching circuit according to the invention; - Figure 5 is a block diagram of a third embodiment of a multi-direction unipolar switching circuit according to the invention; - Figure 6 is a block diagram of the input voltage circuit shown in Figure 5; and - Figure 7 is a table showing the relationship between the

  input voltages and output voltages at the respective terminals

  tives A to D in Figures 5 and 6.

  We now refer to FIG. 1, which represents a block diagram using bipolar transistors as

  amplifying elements. As shown in the figure

  gure, to adapt the impedance of a signal source 10 to the input of the transistor and adapt the impedance of a load 14 to

  the transistor output, it is necessary to connect the

  input and output of the bipolar transistor respectively via an input impedance matching network 11 and an output impedance matching network 12 to obtain the desired performance. Capacitors CB and Cc are respectively used as stop capacitors of the

  DC component at the input and output of the bi-transistor

  BJT polar (from "bipolar junction transistor"). The purpose of these capacitors is to prevent the voltage of the base VB and the voltage of the collector Vc of the bipolar transistor BJT from being influenced by the input and output matching networks 11 and 12. Stop coils of the high frequency component (HF chokes) RFCB ("radio frequency choke") and RFCC are used to prevent AC signals from being influenced by the DC circuit of Figure 1. The parameters Zin and Zout represent respectively

  the input impedance and the output impedance of the bi-transistor

BJT fleece.

  Those skilled in the art can use other polarity circuits.

  change or change the values of CB, CC, RFCB and RFCC to

4 2721155

  make some or all of the impedance matching networks to reduce the number of elements of these matching networks. In addition, the type of bipolar transistor BJT employed has a characteristic such that when its bias voltage is in the linear part of the voltage-current characteristic curve (characteristic V-I), such a transistor has an amplification function. for high frequencies and has

  specific Zin and Zout input and output impedances.

  When it is polarized in the cut-off part of the V-I curve, the transistor no longer has the amplification function and the impedances Zin and Zout are close to infinity (this is due to the

  fact that when the PN junction of the bipolar transistor is po-

  in the opposite direction, the reverse saturation current flowing through the junction is very low and

impedance is Z = V / I).

  Consequently, the present invention uses the features

  of the bipolar transistors indicated above, that is to say the fact that the transistor amplifies the signals when its operating point is located in the linear part, while when it is located in the breaking domain, the Zin and Zout impedances are extremely high,

  to make a switching circuit. Most manufacturers

  cants of high frequency transistors are currently able to effectively control the quality of the transistors they

  manufacture, so that the values of the parameters of the trans-

  sistors do not vary much from copy to copy in

  the mass production of these components.

  When designing high frequency switching circuits, it is necessary, on the one hand, to make a good impedance matching between the input and the signal source and between the

  output and the load when the signal is transmitted, to re-

  reduce signal losses. However, the use of transistors as switching elements, under good conditions

  adaptation during signal transmission, can not only-

  mentally eliminate signal loss, but also provide signal gain. On the other hand, transistors are capable of rejecting unwanted signals so as to have good separation of the signal when they are blocked. Using the characteristic of transistors to have a high impedance

  in the cut-off range, a state of mismatch can be obtained

  tation between the signal source and the switching circuit so that the signal is reflected and, therefore, prevented from

  enter the switching circuit.

  It is also possible to add a switch between the switching circuit and the signal source of the present invention so that, when the transistor of the invention is blocked, the signal source is switched to a dummy load for

  eliminate the mismatch of the signal source. Such a pro-

  assigned also falls within the scope of the invention.

  Another feature of the present invention is that, as shown in Figures 2

  and 5, the invention uses a plurality of bipolar transistors

  laires (BJT1 and BJT2 in Figure 2, and BJT1 to BJT4 in Figure

  gure 5) as switching elements, each of which is connected to a respective input impedance matching network (31 and 32 in FIG. 2 and IMN1 (from "input matching network") to IMN4 in FIG. 5) , and there is only one output impedance matching network (element 36 in FIG. 2 and OHMN (from "output matching network") in FIG. 5) connected to the outputs of all the transistors. This is because if each

  transistor had its own impedance matching network in-

  dependent, there would be interference between the individual output impedance matching networks and it would be difficult to calculate the values of the elements of each network

  impedance matching. The invention takes advantage of the characteristics

  transistors, which have a high output impedance

  tie in the off state and ensures that only one transistor at a time is in the operating range, and connects the output of

  each transistor has a common junction point (junction point

  tion J in Figures 2, 4 and 5). Consequently, the output impedance at the junction point J of the switching circuit of the invention is very close to that of a single transistor, so that only the parameters of one of the transistors are to be considered during the design. of the output impedance matching network 36. Another advantage of the invention is

  that the number of elements required in the adaptation circuit

  impedance is reduced to reduce bulk and

cost of the switching circuit.

  In the embodiment of FIG. 2, when the transistor BJT1 operates in the linear domain and the

  transistor BJT2 is blocked, by means of bias voltages

  tion controlled by a voltage control circuit

  polarization ions 35, the circuit of FIG. 2 is equivalent

  slow to that of Figure 3. In this situation, the input and

  the output of transistor BJT2 are considered to be open.

  Consequently, the signal from the signal source 33 can enter the input impedance matching network 31 and is amplified by the transistor BJT1 and is then applied to the load 37 via the network. output impedance matching 36 without being influenced by the other

  transistor BJT2. On the other hand, the signal from the source of si-

  gnaux 34 is reflected by transistor BJT2 and cannot

  be amplified by this transistor BJT2. In this way, the cir-

  switching circuitry of the invention can amplify desired signals and reject unwanted signals, and therefore works

  as a two-way unipolar high frequency switch

  tions with good signal separation.

  FIG. 4 represents a second embodiment of the invention, in which N-channel junction field-effect transistor (JFET) field effect transistors, JFET1 and JFET2, are used as amplifier elements,

  and a switch 41 is used in place of the com-

  polarization voltage command 35 of FIG. 2 for com-

  order the bias voltages. It should be noted that the trend

  polarization sion Vss is a negative voltage which is lower than

  lower than the pinch voltages Vp1 and Vp2 of the transistors

  JFET1 and JFET2, respectively. When the switch 41 ap-

  plique the voltage Vss at the point of application of the DC gate voltage (point K in FIG. 4) of the transistor JFET1, the transistor JFET1 is blocked and therefore ceases to amplify the signal coming from the signal source I / P1. At this time, the signal from the I / P2 source enters the JFET2 transistor via an input adaptation circuit IMN2 and is amplified by the JFET2 transistor and supplied by the output thereof. an OMN output impedance matching network without interfering with the signal from the I / P1 signal source. The JFET junction field effect transistors used

  in the embodiment described above are biased

  automatic tion and it should be easy for the skilled person to

  determine the values of the RD, RG, RS and CS parameters required

  to polarize the JFET transistors so as to

  operate in the desired domain.

  Figure 5 shows the block diagram and process

  for controlling a single-frequency high-frequency switching circuit

  four-way area using BJT bipolar transistors as switching elements. In this figure, the points A, B, C, and D represent the respective points of application of the direct voltage of the base of the switching elements BJT1 to BJT4. Due to the presence of the HF RFC choke coil, the DC voltages applied to these points are well insulated and do not influence the high frequency AC signal. If the voltage applied to any one of these points falls below the base-to-transmitter voltage, or "release", VBE (with a typical value of 0.7 V),

  the BJT transistor corresponding to this point is blocked.

  The switching circuit of Figure 5 uses five com-

  voltage trimmers Q1 to Q5 to control the voltages

  larization applied to transistors BJT1 to BJT4, as shown in FIG. 6. The circuit of the invention is designed according to the active low excursion characteristic of the

  voltage comparators, which are open when invaded

  covered, and are grounded when enabled, so that a single BJT bipolar transistor is turned on and the

  rest of the transistors are blocked when a voltage

  taken in the range of 0 to Vcc is applied. The relation between the control voltages and the state of the transistors is

  indicated in the table in figure 7. The voltage comparator

  sion normally used in the invention is the comparator n '

  LM 339, which is commercially available.

  In addition to being the polarization resistors of the trans

  BJT bipolar sistors, resistors R1 and R2 of figure 5

  are also the high excursion resistances of the compara-

ters Q1 to Q6.

  When one or more active low excursion elements are connected to a high excursion resistance and when one of them is enabled, the voltage at the junction point goes to low level. This type of circuit configuration is called "wired AND". Comparators Q2, Q3, Q4 and Q5 in Figure 6

  are mounted in AND wired configuration.

  The circuit of the invention can be mounted in wired AND,

  as shown in figure 6, to obtain a cir-

  more flexible control baking so that each

  BJT bipolar sistor can be controlled by ac elements

  multiple low excursion devices, and each active low excursion element can be connected to different switches, transducers and logic circuits. Compared to well known relay or PIN diode circuits, the present invention is

  easier to connect to external devices.

9 2721155

  The four-way unipolar switch of the figure of the invention has great commercial value for the reception of satellite television signals. Since the bandwidth of "general public" satellite receivers is limited and the number of satellites and programs

  increases almost day by day, coaxial cables sup-

  may be required for each satellite to receive signals from the satellite after the signal has been lowered by a low noise frequency changer. In addition, most satellite program viewers use only one coaxial cable to connect the outdoor antennas (more than two antennas) to the receiver. By

  Therefore, the logical solution is to switch the different

  satellite signals using a high frequency switch

  multiple entry quence. Now the high frequency switch

  unipolar with several directions according to the invention is exact-

  the best choice for this. The invention has the following advantages: (a) the proposed circuit provides a gain to compensate for the losses of the signal and has good separation of the signals; (b) the circuit has greater reliability and a longer service life than that of the conventional relay circuit; (c) the circuit requires fewer elements than the PIN diode circuit, and the structure of the circuit is much simpler since it does not require compensation amplifiers and

  only one output impedance matching network is needed

  saire; (d) the cost of the circuit is low; and (e) the circuit is easy to connect to different sources of control signals since each bipolar trnaisistor can

  be controlled by an AND wired function.

  A multipolar switching circuit with several directions can be produced by combining a number of unipolar switching circuits with several directions of

  the invention. It goes without saying that the multiswitch circuit

  tipolar in several directions does not depart from the scope of the invention.

  Since different embodiments of the information

  vention can be made without departing from the scope thereof, it will be understood that all the explanations given here and the figures shown in the accompanying drawings are given only by way of illustration and should not be interpreted as limiting the invention. Therefore, it will be understood that

  the drawings are only an example of a pre-

fairy of the invention.

il 2721155

Claims (4)

Claims   1. High frequency unipolar multi-directional switch   tions, characterized in that it comprises: - a plurality of inputs; - A plurality of switching means in the same number as the inputs, each comprising: an input impedance matching network connected to one of the inputs; and a transistor, an input electrode of which is connected to the output of the input impedance matching network; - a junction point connecting all the outputs of the switching means;   - a single output impedance matching network connected to-   said junction point; and - a DC voltage bias network for supplying bias voltages to the respective transistors such that when switching a certain input signal, only one of the transistors operates in the field   linear, and the others are blocked.   2. Unipolar high frequency switch with several directions   tions according to claim 1, characterized in that said transistors are bipolar transistors and are mounted in common transmitter.   3. High frequency unipolar multi-directional switch   tions according to claim 2, further comprising a plura-   lity of low excursion elements each connected to a point of application of a DC voltage applied to the base of each of the transistors, characterized in that one or more of the low excursion elements serves to bring the voltages of the base of the transistors below the bias voltages of   these to force the transistors to operate in the do- 12 2721155 main cut.   4. High frequency unipolar multi-directional switch   tions according to one of the preceding claims, characterized   in that it is used to switch a number of si-   satellite signals to a satellite signal receiver.