Amplifiers – With semiconductor amplifying device – Including differential amplifier
Reexamination Certificate
2000-04-12
2001-04-17
Pascal, Robert (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including differential amplifier
C330S261000
Reexamination Certificate
active
06218899
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to amplifier circuits and to amplifiers which are used in tuners and even more specifically to such amplifiers where variable-gain low noise amplification is required.
BACKGROUND
U.S. Pat. No. 5,737,035 dated Apr. 7, 1998, shows a tuner circuit. The front end of such a tuner requires a broadband, highly linear Variable-gain Low Noise Amplifier (VLNA). The VLNA's input comes from either an antenna for wireless broadcasts or from a coaxial cable for cable transmission. The output of the VLNA supplies the input of the first up-converting mixer. The noise figure specification for the VLNA is highly critical, and has the highest impact on the overall noise figure of the system. Non-linearities of the amplifier also have a large effect on the proper operation of the tuner.
LNA's are typically used to meet cellular requirements, which are narrow-band. However, a television tuner must receive carriers from 50 MHZ to over 860 MHz. A narrow bandwidth system also has less stringent linearity specifications because fewer intermodulation distortion products fall in-band. Finally, because the incoming signal power to a tuner can vary by many orders of magnitude, there is a need for an LNA whose gain is continuously-variable. The gain variability function adds noise, distortion, and complexity to the LNA.
Accordingly, there exists a need in the art for a low noise amplifier which can handle a wide frequency range as well as a wide amplification range.
A further need exists in the art for such a circuit which can be constructed on a single substrate and which will not be effected by, nor produce, noise injection.
SUMMARY OF THE INVENTION
These and other objects, features and technical advantages are achieved by a system and method which meets the noise, linearity, and gain ranges required in wideband tuners by using a segmented resistor and MOS structure in the signal path to vary the gain of a bipolar (or MOS) transistor amplifier. The system includes a method for both biasing the device and controlling the gain using a differential voltage input. Both PMOS, and NMOS transistors are used and operated in their triode mode to preserve linearity and low noise. The circuit operates for transmission signals received via air wave broadcast or via cable and can handle wide ranges of amplification requirements as well as intermodulation constraints.
It is a technical feature of my invention to provide a VLNA which utilizes a pseudo differential structure to reduce the effects of on-chip substrate injection and supply line fluctuations.
It is another technical feature of my invention to provide a circuit where the gain of the amplifier changes in a linear and predictable fashion with the controlling voltage input.
It is a further technical feature of my invention that such a circuit is constructed to produce a large gain range, having low noise, capable of operating across a wide bandwidth.
It is a further technical feature of my invention to provide such a circuit and method which is self biasing.
It is a further technical feature of my invention to provide such a circuit which will operate with circuits which require either a high constant output intercept or a high constant input intercept.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
REFERENCES:
patent: 3761741 (1973-09-01), Hoeft
patent: 4929908 (1990-05-01), Imanishi
patent: 5610557 (1997-03-01), Jett, Jr.
Choe Henry
Fulbright & Jaworski L.L.P.
Microtune ( Texas), L.P.
Pascal Robert
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