Technique to generate negative conductance in CMOS tuned...

Details Technique to generate negative conductance in CMOS tuned... Technique to generate negative conductance in CMOS tuned...

1999-09-13

2001-09-18

Pascal, Robert (Department: 2817)

Amplifiers

With semiconductor amplifying device

Including frequency-responsive means in the signal...

C330S305000

Reexamination Certificate

active

06292060

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to printed and integrated circuits and in particular to integrated CMOS tuned RF amplifiers.
2. Description of Related Art
Advances in CMOS technology has made it possible to integrate onto a single chip a communication system operating in a frequency range between 0.9 and 2.5 GHz which can be used in mobile phones and global positioning systems. An important aspect of the communication system is having a low noise amplifier (LNA). The prime objective of the LNA is to produce a signal at a given noise figure for a minimum expenditure of power. Since an LNA is a first stage of a receiver, the overall design will be dominated by the noise figure. When the gain of the LNA is large, noise contribution by subsequent stages becomes insignificant. Also a narrow bandwidth LNA provides increased immunity for low frequency base band signals.
In U.S. Pat. No. 5,861,778 (Louagie et al.) a low noise amplifier is based on a differential difference amplifier having a differential output with two pairs of differential inputs. This is done to minimize harmonic distortion. In U.S. Pat. No. 5,710,523 (Kobayashi) a low noise amplifier utilizing a high mobility transistor and a tunable heterojunction bipolar transistor is described. In U.S. Pat. No. 5,642,080 (Whang et al.) a low noise amplifier is described that includes an input impedance component consisting of an inductor and a capacitor. Two MESFETs are connected in cascade with a capacitor connected between them to enhance the stability of the amplifier. In U.S. Pat. No. 5,574,405 (Razavi) a low noise amplifier is combined with a mixer and synthesizer circuit to produce an RF system front end. The synthesizer shares power with the low noise amplifier to reduce power consumption. In U.S. Pat. No. 5,488,382 (Fenzi et al.) a low noise amplifier with high input impedance is described using a cascode pair of FET transistors. A feedback is provided from output to input to lower the Q of the antenna at the input of the amplifier, broadening the bandwidth of the detector and matching the antenna to the noise factor of the amplifier.
A common source tuned RF amplifier is frequently used as a low noise amplifier. Using a cascode amplifier as an input stage isolates an inter stage tank circuit from any input matching networks which can improve stability. An integrated inductor which forms a part of the tank circuit has a low Q (quality factor) which limits the Q of the LNA amplifier. The gain and Q of the LNA can be enhanced by adding a negative conductance at the output of the LNA to the tank circuit, but this usually means added active devices which results in more noise and more power dissipation.
SUMMARY OF THE INVENTION
In this invention a single capacitor is added to a cascode low noise amplifier to produce a negative conductance and increase the Q and gain, as well as improve the noise performance of the amplifier. An LC tank circuit is connected to the drain of the output transistor of the cascode amplifier, and the added capacitor is connected from drain of the output transistor to the drain of the input transistor. The capacitor between the two drains produces a negative conductance which when combined with the LC tank circuit produces a higher amplifier Q and gain. The added capacitor being passive does not generate noise or add additional power to the amplifier, and enhances the characteristics of the low noise amplifier by providing better gain without additional power consumption. The higher Q allows the low noise amplifier to perform some bandpass functions.
The LC network connected to the drain of the output transistor of the LNA (low noise amplifier) is designed to produce a peak gain at the center frequency of the amplifier. The added capacitor connected between the drains of the cascode transistors of the LNA is chosen to produce a maximum gain. The value of the added capacitor creates a negative conductance which when combined with the LC tank circuit increases the Q and gain of the LNA and shifts the center frequency of the amplifier. The capacitor of the LC tank circuit is adjusted to return the center frequency to the required design point producing a high Q and gain for the LNA.
The techniques of this invention are applicable in tuned RF amplifiers developed from a wide range devices and technologies. Devices such as BJT, MESFET, HBT and HEMT can be used to form tuned RF amplifiers using similar tuning techniques disclosed in this invention. These devices can be constructed using various processes and technologies such as CMOS, BJT, BiCMOS, SIGe and SOI.


REFERENCES:
patent: 3805164 (1974-04-01), Callaway
patent: 4409557 (1983-10-01), Sechi
patent: 4663599 (1987-05-01), Patch
patent: 5142239 (1992-08-01), Brayton et al.
patent: 5488382 (1996-01-01), Fenzi et al.
patent: 5574405 (1996-11-01), Razavi
patent: 5642080 (1997-06-01), Whang et al.
patent: 5710523 (1998-01-01), Kobayashi
patent: 5861778 (1999-01-01), Louagie et al.
patent: 6127886 (2000-10-01), Khabbaz et al.

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