Telecommunications – Transmitter – Modulation by absorption – shielding – or reflecting
Patent
1996-06-26
1998-10-13
Crosland, Donnie L.
Telecommunications
Transmitter
Modulation by absorption, shielding, or reflecting
455 47, 455104, 455109, 332170, H03C 152, H04B 168
Patent
active
058226850
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a circuit arrangement in particular, although not exclusively, for use with a pseudo passive transponder (PPT).
Conventionally PPT's use a diode detector arrangement to detect an incoming signal from an interrogating source. The diode can be operated as a modulated reflector by modulating the incoming signal with information and reflecting it back to the interrogating source. The reflected signal is however of reduced amplitude with respect to the incoming signal which limits the useful range of the transponder. In addition the reflected signal has a double sideband which increases the complexity of the circuitry required at the interrogating source and reduces the spectral efficiency of the system. A need exists therefore for a circuit arrangement for use in a PPT which can be made available at relatively low cost, which can increase the available operating range, and preferably emit energy with only a single sideband.
SUMMARY OF THE INVENTION
This invention provides a circuit arrangement comprising a transistor configured to detect an amplitude modulated signal upon operation within the non-linear relatively low gain region of the transistors current/voltage characteristic, the transistor also being configured by means of a feedback arrangement upon operation within a linear relatively higher current and gain region of the characteristic to reflect the signal with an increased amplitude.
Surprisingly, the applicants have found that a single transistor can be used both as a so called "cold cathode" detector and a reflective amplifier merely by changing the operating conditions of the transistor. As compared to the known diode arrangement, there need not be a significant increase in power consumption.
In a preferred embodiment, the transistor is a field effect transistor (FET) which is switchable between the detect and reflect modes by increasing the drain/source current. With such a device, when operated at microwave frequencies, the feedback can be provided via the intrinsic capacitance between the gate and source of the FET.
According to another aspect of the present invention there is provided a modulated reflector circuit arrangement comprising a transistor configured by means of a feedback arrangement upon operation within a linear region of the transistor's current/voltage characteristic to reflect an incoming amplitude modulated signal with an increased amplitude and modulating means operable to modulate power to the transistor with a periodic waveform in which the reciprocal of the period of the periodic waveform is the required sideband frequency of the reflected signal and the waveform is selected such that the arrangement reflects a substantially single sideband signal.
BRIEF DESCRIPTION OF THE DRAWING
In order that the invention may be well understood, embodiments thereof will now be described by way of example with reference to the accompanying drawings, in which;
FIG. 1 is a schematic circuit diagram of a circuit arrangement;
FIG. 2 shows a typical voltage/current characteristic of a FET;
FIG. 3 shows the detected signal in another mode of operation; and
FIG. 4 is a circuit diagram of a circuit arrangement for use at UHF frequencies.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As shown in FIG. 1 a circuit arrangement comprises a field effect transistor 1, which can for example be either a silicone JFET or a GaAs device, depending on the required operating frequency. An antenna 2 supplies a signal via a matching network 3 to the gate 1.sub.g of the transistor. The drain 1.sub.d is connected via a bias network 4 to a power supply 13 producing a rail voltage V.sub.d. The bias conditions on the gate side are set by means of an appropriate bias network 5 connected to a voltage rail V.sub.g. The source 1.sub.s is connected via a bias network 6 to a variable current source 7 which is itself connected to a control circuit 8. The bias networks 4, 5, 6 provide isolation between the relatively low voltage, low frequency signals on th
REFERENCES:
patent: 3480951 (1969-11-01), Freedman
patent: 4591803 (1986-05-01), Saleh
patent: 4768000 (1988-08-01), Pavio, Jr. et al.
patent: 4978932 (1990-12-01), Gupta et al.
patent: 4980689 (1990-12-01), Kawakami
patent: 5305469 (1994-04-01), Camiade et al.
patent: 5319802 (1994-06-01), Camiade et al.
Crosland Donnie L.
GEC - Marconi Limited
LandOfFree
Modulating reflector circuit does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Modulating reflector circuit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Modulating reflector circuit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-326549