Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
  • H03K17/51—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used
  • H03K17/56—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices
  • H03K17/687—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being field-effect transistors
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
  • H03K17/51—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used
  • H03K17/56—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices
  • H03K17/687—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being field-effect transistors
  • H03K17/6871—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being field-effect transistors the output circuit comprising more than one controlled field-effect transistor
  • H03K17/6874—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being field-effect transistors the output circuit comprising more than one controlled field-effect transistor in a symmetrical configuration
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
  • H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
  • H04B1/40—Circuits
  • H04B1/44—Transmit/receive switching
  • H04B1/48—Transmit/receive switching in circuits for connecting transmitter and receiver to a common transmission path, e.g. by energy of transmitter

Definitions

• PCT patent application WO99/55085 discloses a video recorder with an RF switch that is provided with a first capacitor, a main current channel of a field effect transistor and a second capacitor coupled successively between the input and output.
• the gate of the field effect transistor is grounded.
• a resistor is provided between a control input and an internal node between the first capacitor and the main current channel of the transistor.
• the main current channel of the transistor can be made conductive or non-conductive, dependent on whether the RF switch should be turned on or off.
• a normally-on transistor is used (which is conductive when no voltage difference is present between gate and source).
• an object of the invention to provide an apparatus having a signal switch which can be controlled with a less complicated circuit that passes signals when no power is supplied to the switch.
• the invention provides an apparatus as set forth in claim 1.
• a switch is realized that is "on" when no power supply voltage is applied.
• the signal switch 10 contains a first field effect transistor 100, a second field effect transistor 102, a diode 104, a decoupling capacitor 105, a resistor 106 and a pair of capacitors 108a,b.
• the first and second transistors are of the "normally-on" type (depletion transistors), that is, they have a negative threshold voltage so that the main current channel conducts when the potential difference between the control electrode and the main current channel is zero.
• the main current channel becomes isolating (substantially without induced mobile charge carriers) only when the potential of the control electrode is at a potential more than a threshold below the potential of the main current channel.
• transistors with a threshold of -3.5 Volts may be used (that is, a relatively large threshold voltage, so that the transistor is solidly on, with a low channel resistance, when the gate-source voltage is zero.
• a high threshold voltage is possible because the diode 104 is not connected in parallel with the gate-source of the transistors, as far as DC voltages are concerned).
• the diode 104 is preferably a silicon "PIN" diode, which has a low junction capacitance when it is reverse-biased. (PTN refers to the doping profile, which has a substantially undoped intrinsic region between the anode and the cathode of the diode.)
• a signal input 18a of the switch 10 is coupled to a signal output 18b (which forms the output 18b) via, successively, a first one 108a of the capacitors, the main current channel of the first field effect transistor 100, an internal node 101, the main current channel of the second transistor 102 and a second one of the capacitors 108b.
• the control electrodes of the first and the second field effect transistor 100, 102 are coupled to a common conductor 107.
• the resistor 106 is coupled between the internal node 101 and this common conductor 107.
• An output of the control circuit 12 is coupled to the common conductor 107 and to the internal node 101, the latter via diode 104 in the forward direction. This output of the control circuit 12 is coupled to the common conductor 107 via decoupling capacitor 105.
• an RF signal is received by antenna input 14.
• processing system 16 When processing system 16 is active, it processes the signal and produces an output signal that is applied to output 18b.
• processing system 16 controls control circuit 12 to make signal switch 10 block this signal.
• Control circuit 12 realizes this by applying a positive voltage of, for example, 5 Volts to the anode of diode 104, relative to common conductor 107, forward- biasing the diode 104. This results in application of a positive voltage to intemal node 101 relative to the common conductor 107.
• This positive voltage is equal to the voltage at the anode of the diode minus a voltage drop across the diode 104, which is approximately 0.7 Volts in the case of a silicon diode, so that the voltage difference between the internal node and the common conductor 107 is, for example, 4.3 Volts.
• the voltage of the control electrodes of the first and second transistors 100, 102 is substantially below that of the main current channels of the first and second transistors 100, 102, causing conduction through the main current channels of these transistors to be cut off.
• the diode 104 is forward-biased, causing it to have a low dynamic resistance, which is coupled to the common conductor via decoupling capacitor 105.
• an "off state of the signal switch 10 is realized in which the main current channels of transistors 100, 102 and diode 104 form a T- type attenuator between input 18a and output 18b with a large attenuation factor.
• this "on" state of the signal switch 10 does not require any voltage difference to be applied to the signal switch 10.
• the on-state can be realized without a need for a voltage difference from a supply voltage source.
• the on-state may also be realized when a supply voltage difference is present, by applying a zero- voltage difference between the anode of diode 104 and common conductor 107 (or more generally a voltage difference that is smaller than the voltage needed for forward-biasing diode 104), on a command from processing system 16, when it is needed to pass the signal from the input 18a to the output 18b.
• Resistor 106 is primarily used to determine the current through diode 104 when this diode 104 is forward-biased.
• This current is preferably made sufficiently high to ensure a sufficiently low dynamic resistance of diode 104 in the off-state of switch 10.
• parasitic resistances may be used instead of resistance 106.
• a diode 104 with a small diode capacitance is preferably used, such as a PTN diode.
• Capacitors 108a,b serve to isolate the internal node 101 from the input and output 18a,b. Thus, control of the switch 10 is made independent of any DC voltages at the input 18a and output 18b.
• capacitors 108a,b may be omitted when no DC voltage is applied to the input and output 18a,b, or when the applied DC voltage does not affect operation of the switch 10.
• Decoupling capacitor 105 need not be present explicitly, its function may be provided, for example, by the power supply of the circuit. However, for high-frequency signals, an explicit decoupling capacitor 105 is preferably used. As shown in Fig. 1, a common conductor 107 is used both for applying voltages to the control electrodes of transistors 100, 102 and as a common terminal for signal input and output, but of course these need not be directly connected. Instead, decoupling capacitor 105 may be coupled to the common terminal for signal input and output, and the control electrodes of the transistors and resistor 106 may be coupled to an internal common conductor 107.
• diode 104 and resistance 106 could be exchanged, so that diode 104 is arranged between internal node 101 and common conductor 107 with its anode connected to the internal node 101, and resistance 106 is coupled between the output of control circuit 12 that is not connected to the common conductor 107 and the internal node 101.
• the voltage difference between the control electrodes of transistors 100, 102 and their main current channels is equal to the forward bias voltage of diode 104 in the off-state of the switch.
• the threshold voltage of the transistors 100, 102 must be in the narrow range between zero and this forward bias voltage. A low threshold voltage is needed in this alternative, resulting in a higher resistance and higher losses. Also, the value of the threshold voltage is much more critical in this alternative.

Landscapes

• Electronic Switches (AREA)
• Burglar Alarm Systems (AREA)
• Stereo-Broadcasting Methods (AREA)
• Amplifiers (AREA)

Priority Applications (7)

Applications Claiming Priority (2)

Publications (1)

Family

ID=27741200

Family Applications (1)

Country Status (9)

Cited By (2)

Families Citing this family (3)

Citations (2)

Family Cites Families (13)

• 2003
  • 2003-01-21 CN CNB038045036A patent/CN1288842C/zh not_active Expired - Fee Related
  • 2003-01-21 JP JP2003570466A patent/JP2005518698A/ja active Pending
  • 2003-01-21 WO PCT/IB2003/000172 patent/WO2003071680A1/en not_active Ceased
  • 2003-01-21 AT AT03742616T patent/ATE449461T1/de not_active IP Right Cessation
  • 2003-01-21 KR KR1020047013167A patent/KR100974107B1/ko not_active Expired - Fee Related
  • 2003-01-21 US US10/505,269 patent/US7268606B2/en not_active Expired - Fee Related
  • 2003-01-21 DE DE60330121T patent/DE60330121D1/de not_active Expired - Lifetime
  • 2003-01-21 AU AU2003201127A patent/AU2003201127A1/en not_active Abandoned
  • 2003-01-21 EP EP03742616A patent/EP1481478B1/en not_active Expired - Lifetime

Patent Citations (2)

Non-Patent Citations (1)

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