Amplifiers – Combined with automatic amplifier disabling switch means
Reexamination Certificate
1999-09-07
2001-04-03
Pascal, Robert (Department: 2817)
Amplifiers
Combined with automatic amplifier disabling switch means
C330S009000, C330S110000, C330S151000
Reexamination Certificate
active
06211729
ABSTRACT:
BACKGROUND
The present invention concerns circuits used for communication systems and pertains specifically to a circuit that includes an amplifier and a bypass switch useful for low power devices that utilize microwave signals.
Modem digital wireless systems, such as those used in cellular phones and local area networks (LANs) utilize signals with a frequency typically in the range of 0.5 gigahertz (GHz) to 6.0 GHz.
For strong transmission signals, for example when there is a relatively short transmission distance, it is often advantageous to use a switch or series of switches to bypass a microwave amplifier in order to conserve power. The microwave amplifier, while important to achieve high dynamic range for weak transmission signals, may be unnecessary for strong transmission signals. Providing a bypass of the microwave amplifier allows the system gain to be lowered down when the input signal is strong.
In the prior art, to provide for the bypass of a microwave amplifier, switch components are mounted on a printed circuit board. The switch components route the signal to the amplifier to perform the basic amplification function or to the output. Each switch component is, for example, a mechanical type switch, a solid state field-effect transistor (FET) switch or multiple diodes functioning as a switch. A typical topology of an amplifier with a bypass switch includes three switches. A bypass switch is use to bypass the amplifier. A switch connected to the input of the amplifier and a switch connected to the output of the amplifier are used to isolate the amplifier when the bypass switch is turned on and the amplifier is being bypassed.
One disadvantage of the above-described prior art topology is that every switch and the amplifier requires a separate bias/control circuit. In addition several components must be used to build each switch and amplifier, complicating the system design and using up valuable space. Mechanical switches require high voltage levels (15V or more) and are slow in switching speed. Diode switches require that current be wasted to turn them on and off and require numerous DC bias elements. While switches could be integrated with the amplifier into a single integrated circuit (IC), the control and signal degradation due to parasitic capacitances within such an IC could degrade the performance of the IC.
Ray Moroney, Kevin Harrington, Wayne Struble, Brian Khabbaz, Mike Murphy,
A High Performance Switched
-
LNA IC for CDMA Handset Receiver Applications,
1998 IEEE Radio Frequency Integrated Circuits Symposium, p. 43-46, shows an integrated Gallium Arsenide (GaAs) FET solution where a switch function is integrated with an amplifier. However, the disclosed circuit uses an external control for the switch function. Additionally, the disclosed amplifier/switch uses only a series mode switch. Also, the disclosed circuit uses several blocking capacitors that increase die size and cost.
SUMMARY OF THE INVENTION
In accordance with the preferred embodiment of the present invention, an amplifier/switch circuit includes a first circuit input, a second circuit input, a circuit output, an amplifier, a switching circuit and a DC blocking capacitor. The amplifier has an amplifier control input, a first amplifier output and a second amplifier output. The amplifier control input is connected to the first circuit input. The first amplifier output is connected to the second circuit input. The second amplifier output is connected to the circuit output. A switching circuit has a switch control input, a switch input and a switch output. The switch control input is connected to the circuit output. The control input is connected to the second circuit input. The DC blocking capacitor is connected between the amplifier control input of the first transistor and the switch input.
In the preferred embodiment, a resistance is connected between the second circuit input and the circuit output. A feedback resistance is connected between the second amplifier output of the first transistor and the input of the switching circuit. For example, the switching circuit comprises three transistors connected in a series-shunt-series configuration.
Using the present invention, only three terminals are required to implement an amplifier/switch circuit. The first circuit input operates to receive a high frequency signal and provides a DC reference. The second circuit input serves as a high frequency ground, and as a DC control voltage to place the amplifier/switch circuit in a through mode. The amplifier/switch circuit places the amplified signal on the circuit output. The DC power supply is also placed on the circuit output.
When the amplifier/switch circuit is in gain mode, the amplifier/switch circuit amplifies the signal from the circuit input to the circuit output. When the amplifier/switch circuit is in through mode, the amplifier/switch circuit goes automatically to zero current and routes the signal on the circuit input to the circuit output with minimal loss.
The disclosed embodiment of the present invention offers several advantages over the use of several discrete components to duplicate this function. The primary advantages are small size, low cost, ease of use, ease of implementation and zero current draw during through mode operation.
The disclosed embodiment of the present invention also is advantageous over the integrated GaAs FET solution discussed above in the Background section. For example, a series-shunt-series combination of field effect transistors (FET) overcome several potential radio frequency (RF) problems in the integrated GaAs FET solution discussed above. The series-shunt-series combination of transistors also provides improved isolation resulting in greater circuit stability over a wide frequency range. The higher isolation (on the order of 25 dB at microwave frequencies) allows for greater gain. This isolation contributes to increasing performance of the amplifier/switch circuit allowing the amplifier section to operate to higher frequencies, for example up to proximately 8 GHz. In addition, the feedback resistor in the preferred embodiment helps RF performance and also provides a DC pull-up resistor of the transistors connected in series. The disclosed embodiment of the amplifier/switch circuit can be used in a simple three lead package, which offers many RF and microwave performance advantages.
REFERENCES:
patent: 5459428 (1995-10-01), Kim et al.
patent: 5796300 (1998-08-01), Morgan
patent: 5880630 (1998-08-01), Iwamoto et al.
Ray Moroney, Kevin Harrington, Wayne Struble, Brian Khabbaz, Mike Murphy, A High Performance Switched-LNA IC for CDMA Handset Receiver Applications,1998 IEEE Radio Frequency Integrated Circuits Symposium, p.43-46.
Frank Michael Louis
Morkner Henrik
Agilent Technologie,s Inc.
Nguyen Patricia T.
Pascal Robert
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