Telecommunications – Receiver or analog modulated signal frequency converter – Frequency modifying or conversion
Reexamination Certificate
1999-01-29
2001-03-20
Bost, Dwayne (Department: 2681)
Telecommunications
Receiver or analog modulated signal frequency converter
Frequency modifying or conversion
C455S318000, C455S319000, C455S323000, C455S325000, C455S326000, C455S330000
Reexamination Certificate
active
06205324
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to frequency conversion devices, such devices commonly known as mixers, and, in particular, broadband double-balanced mixers.
BACKGROUND OF THE INVENTION
A mixer is a device that converts signals from one frequency to another. This is accomplished by applying a local oscillator (LO) reference signal to one of the mixer ports, and the signal to be converted to a second mixer port. The sum and difference frequencies of the two signals are predominantly what appear at the mixer output port, although the sum and difference frequencies of the harmonics of the two input frequencies also co-exist on the mixer output port as well. For transmitter applications, a low frequency signal is first processed (or modulated) and then up converted through a mixer to a microwave frequency, where it is usually amplified and transmitted. For receiver applications, the received signal is down converted through a mixer to a low frequency where the information is extracted (demodulated).
The diode, a non-linear device, creates the mixing action in a mixer. Diodes, the simplest kind of semiconductor, consisting simply of a package with two leads, permit current flow in one direction only. Like any semi-conductor, a diode is capable of handling only a limited amount of input signal power before it saturates.
A mixer's dynamic range is the input power range over which a mixer is usable. On the low input power end, it is limited by the noise figure and other system parameters such as signal to-noise ratio and receiver bandwidth. On the high end it is limited by either the saturation level or the input level for which certain spurious signals reach unacceptable levels.
To cover a broad range of frequencies, combinations of mixers have been used in order to get adequate coverage. This results in disadvantageous bulk and cost. Instrumentation design reflect a compelling tendency toward remote instrument heads. There is a need for a mixer capable of operating across broad RF and local oscillator frequency bandwidths to meet the design and performance requirements .
SUMMARY OF THE INVENTION
The invention provides a frequency conversion device operable across very broad RF and local oscillator frequency bandwidths.
The invention provides a broadband double-balanced mixer with improved performance and reliability at lower manufacturing cost and greatly reduced size and weight. The invention further provides a highly portable broadband mixer suitable for placement on a remote instrument head.
The invention provides an embodiment wherein the device design permits reducing the number of parts from more than 40 down to about 4, thereby eliminating the losses associated with a greater number of parts.
In the preferred embodiment, a Wilkinson-type splitter is positioned between the resistors and the RF source and functions to increase the parallel impedance across the diode at higher frequencies.
This configuration provides for the maintenance of even mode impedance Zoe of the splitter transmission lines at 2Rrf throughout its length. The splitter functions to increase the parallel impedance across the diodes from 2*R to 2*R+2*Z
0
o at higher frequencies where the divider is significantly longer than a quarter wavelength. Increased parallel impedance forces more local oscillator current through the diode, which means a weaker local oscillator drive signal can be used to produce equal diode switching currents. The splitter also provides a matched termination to any LO signal that passes the diode and resistors.
In an alternate embodiment of the invention, two balanced resistors replace a Wilkinson-type splitter. When R
1
=R
2
=R, the lowered impedance removes the lower frequency limit imposed by the Wilkinson-type splitter. The RF signal sees the resistors in parallel for a smaller effective series of resistance of R
2
at all frequencies. The lowered resistance permits more RF energy to reach the diodes.
REFERENCES:
patent: 3665508 (1972-05-01), Gawler
patent: 4035732 (1977-07-01), Lohrmann
patent: 4230956 (1980-10-01), Steinbrecher
patent: 5280649 (1994-01-01), Riebman
patent: 5553319 (1996-09-01), Tanabakuchi
Agilent Technologie,s Inc.
Bost Dwayne
Davis Temica M.
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