Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Accelerating switching
Reexamination Certificate
2000-08-24
2001-10-30
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Gating
Accelerating switching
C327S427000, C327S389000, C327S432000, C333S08100R
Reexamination Certificate
active
06310508
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to high frequency switches, and more particularly, to a high frequency switch that provides a high degree of isolation while maintaining a high bandwidth and economical construction.
BACKGROUND OF THE INVENTION
There are many circuit designs that require a high frequency switch. An ideal switch has very low losses in the “on” mode while providing very high losses in the “off” mode. In both modes, the switch must provide a high degree of isolation in the reverse direction. In addition, the ideal switch has a flat gain over the operating frequency range of the switch and settles quickly after being switched. Finally, cost is always a factor in switch design. The ideal switch should have a low part count and have as few control lines as possible to prevent switch-to-switch crosstalk in circuits employing multiple switches.
Mechanical switches can provide many of these desirable features. However, such switches have slow switching times and are subject to wear. Accordingly, there are many applications in which mechanical switches cannot be used.
Switches based on PIN diodes in a biased divider configuration followed by a high input impedance amplifier have also been utilized. However, these switches have unsatisfactorily high losses in the “on” state and/or insufficient losses in the “off” state to provide the needed on/off switching ratio for many applications. In addition, these switches generate harmonic distortions. Finally, these switches have a high part count that makes them commercially unattractive for many applications.
Broadly, it is the object of the present invention to provide an improved high frequency switch.
It is a further object of the present invention to provide a high frequency switch that more nearly resembles the ideal switch discussed above than prior art switches.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.
SUMMARY OF THE INVENTION
The present invention is a high-frequency switch for blocking or transmitting a high frequency input signal. The switch includes a common-base transistor having an emitter, base, and collector, the emitter being connected to an input node and the base being connected to a power rail that is preferably ground. The input node is coupled to the input signal. The present invention utilizes a shunt having a switching element with closed and open states to route the input signal either to the collector of the common mode transistor or to the power rail. The switching element connects the input node to the power rail in the closed state and isolates the input node from the power rail when the switching element is in the open state. The open and closed states are selected by the application of a control signal to the switching element. A bias circuit sets the input node to be at a first bias potential when the switching element is in the open state and a second bias potential when the switching element is in the closed state. The first bias potential causes the common-base transistor to be in a conducting state, and the second bias potential causing the common-base transistor to be in a non-conducting state. The switching element may be constructed from a wide variety of circuit elements including a diode, transistor, or mechanical switch.
REFERENCES:
patent: 3731116 (1973-05-01), Hill
patent: 3800229 (1974-03-01), Backwinkel
patent: 3813602 (1974-05-01), Van Dijum et al.
patent: 4019160 (1977-04-01), Kam
patent: 4494076 (1985-01-01), Rinderle
patent: 4689498 (1987-08-01), Rinderle
Agilent Technologie,s Inc.
Cunningham Terry D.
Nguyen Long
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