Telecommunications – Receiver or analog modulated signal frequency converter – Frequency modifying or conversion
Reexamination Certificate
2000-11-27
2003-05-06
Chin, Vivian (Department: 2682)
Telecommunications
Receiver or analog modulated signal frequency converter
Frequency modifying or conversion
C455S118000, C331S1170FE
Reexamination Certificate
active
06560452
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to oscillators and, more particularly, to tunable oscillators having a transistor formed of a wide bandgap semiconductor material.
BACKGROUND OF THE INVENTION
Upconverters and downconverters that include an oscillator, such as a voltage controlled oscillator, a phase locked oscillator or the like, are widely utilized for a variety of applications including signal transmission, signal reception and the like. With respect to commercial applications, upconverters and downconverters are utilized in broadband terrestrial and satellite communication systems, broadcast systems, radar systems and the like. For example, wireless radio systems include an upconverter for upconverting a low frequency baseband signal to a higher frequency for transmission purposes. Likewise, in military applications, upconverters are utilized not only as transmitters, but also as radar jamming devices and the like.
There are two principle types of upconverters for radio frequency (RF) systems, saturated upconverters and linear upconverters. As shown in
FIG. 1
, a saturated upconverter typically includes a phase locked oscillator
12
that receives a reference signal having a relatively low frequency and that produces an output signal having a higher frequency. As known to those skilled in the art and as depicted in
FIG. 2
, a phase locked oscillator typically includes a phase detector/discriminator
12
a
that compares the relative phases of a relatively low frequency reference signal and a feedback signal derived from the output of the phase locked oscillator. The output of the phase detector/discriminator is amplified by a loop amplifier
12
b,
filtered by a loop filter
12
c
and provided to a voltage controlled oscillator
12
d
in order to controllably adjust the output of the voltage controlled oscillator. In particular, the amplified and filtered signal is utilized to controllably alter the bias voltage applied to the transistor of the voltage controlled oscillator. The phase locked oscillator can also include an optional prescalar/divider
12
e
that modifies the output of the phase locked oscillator that is fed back to the phase detector/discriminator. As such, the phase locked oscillator forms a phase locked loop.
A saturated upconverter
10
also generally includes one or more drivers
14
, one or more amplifiers
16
and a solid state power amplifier
18
for substantially amplifying the output signal provided by the phase locked oscillator
12
. Although not depicted, the saturated upconverter can also include a frequency doubling element or the like for altering the frequency of the output signal. Once appropriately amplified, the output signal is provided to an antenna
20
for transmission.
As depicted in
FIG. 3
, a linear upconverter
22
also generally includes a phase locked oscillator
24
, such as depicted in
FIG. 2
, for receiving a relatively low frequency reference signal and for producing an output signal having a greater frequency. A conventional linear upconverter also includes a first mixer
26
for combining an input signal having an intermediate frequency and a signal derived from the output signal of the phase locked oscillator. In this regard, the linear upconverter can include a frequency divider
28
disposed between the phase locked oscillator and the first mixer for reducing the frequency of the output signal of the phase locked oscillator. In addition, the linear upconverter can include one or more drivers
29
between the frequency divider and the first mixer in order to amplify the output of the frequency divider. Thus, the output signal of the phase locked oscillator, following its reduction in frequency and its amplification, serves as a local oscillator signal for the first mixer. The linear upconverter also includes a second mixer
30
for combining the output of the first mixer and another signal derived from the output signal of the phase locked oscillator. As depicted, the linear upconverter typically includes at least one and, more commonly, a plurality of drivers
32
and/or amplifiers between the phase locked oscillator and the second mixer in order to appropriately amplify the output signal of the phase locked oscillator. Although not depicted in
FIG. 2
, some linear upconverters include a frequency multiplier or the like between the phase locked oscillator and the second mixer for increasing the frequency of the output signal produced by the phase locked oscillator prior to its presentation to the second mixer. In any event, the signal derived from the output signal produced by the phase locked oscillator serves as a local oscillator signal for the second mixer. The linear upconverter can further include a solid state power amplifier
34
for amplifying the output of the second mixer prior to transmission by an antenna
36
or the like. Further, the linear upconverter can include filters, such as a first filter
38
disposed between the first and second mixers and a second filter
40
disposed between the second mixer and the solid state power amplifier, for blocking the respective local oscillator signals.
Both types of upconverters are effective for reliably producing RF signals of a predetermined frequency and power level. However, these upconverters are not as efficient as desired. For example, some upconverters produce RF output signals that have only about ten percent of the DC power that was input to the signal source. The relative inefficiency of conventional upconverters is attributable to a number of factors. However, one of the more prominent factors for this inefficiency is the DC power required to bias the plurality of components of the upconverter in order for the components to function as desired. In a saturated upconverter
10
, for example, the phase locked oscillator
12
, as well as each driver
14
, each amplifier
16
and the solid state power amplifier
18
must be appropriately biased by means of a supply voltage and a supply current in order to produce the desired RF output signal. Similarly, in a linear upconverter
22
, the phase locked oscillator
24
, each driver
32
and the solid state power amplifier
40
must be appropriately biased by means of a supply voltage and a supply current in order to produce the desired RF output signal. As such, significant input power is consumed to appropriately bias each of these components, thereby substantially diminishing the efficiency with which these conventional upconverters operate.
Additionally, each component of a conventional upconverter occupies a certain amount of space. As such, upconverters that include a plurality of components, such as a plurality of drivers or amplifiers, will generally be somewhat larger. With increasing emphasis being placed upon the miniaturization of all electrical devices, including upconverters, the space requirements of each additional component of a upconverter disadvantageously limit the extent to which the size of a conventional upconverter can be reduced. Similarly, the bias circuitry required for each of these components requires some additional space, thereby further limiting the extent to which the size of a conventional upconverter can be reduced.
Although the drivers and amplifiers of a conventional upconverter decrease the efficiency of the upconverter and increase the space requirements of the signal source, conventional upconverters require drivers and amplifiers in order to appropriately amplify the signals provided by the oscillator prior to transmission. In this regard, the oscillators utilized by conventional upconverters are formed of traditional semiconductor materials having a relatively small bandgap, such as a bandgap of less than two electron volts (eV). For example, the oscillators of conventional upconverters are generally formed of silicon (Si), gallium arsenide (GaAs) or indium phosphide (InP) which have bandgaps of 1.1 eV, 1.43 eV and 1.34 eV, respectively. Transistors formed of these material systems can be readily fabricated and can offer extremely predict
Appiah Charles N.
Chin Vivian
RF Micro Devices, Inc.
Withrow & Terranova , PLLC
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