Transformer coupled quadrature tuned oscillator

Details Transformer coupled quadrature tuned oscillator Transformer coupled quadrature tuned oscillator

2002-08-20

2003-10-28

Zweizig, Jeffrey (Department: 2816)

Oscillators

With frequency adjusting means

With voltage sensitive capacitor

Reexamination Certificate

active

06639481

ABSTRACT:

Radio Frequency (RF) transceivers typically use some form quadrature modulation to achieve higher spectral efficiency. The two most common transceiver architectures are the direct conversion and heterodyne conversion receivers. A direct conversion receiver requires the Radio Frequency Local Oscillator (RFLO) to generate two output signals, referred to as the in-phase and quadrature carriers, whose relative phases are ninety degrees apart. In applications using a heterodyne receiver, an Intermediate Frequency Local Oscillator (IFLO) generates two signals whose relative phases are ninety degrees apart. However, one limitation of the heterodyne receiver architecture is a need for a significant amount of attenuation at the “image frequency” in the front-end filter and the Low Noise Amplifier (LNA). The amount of attenuation of the “image frequency” is called the image rejection ratio of the filter.
A modification of the heterodyne architecture called the Weaver architecture is commonly used in an integrated receiver to achieve additional image rejection. This architecture requires both the local oscillator at radio frequencies as well as that at intermediate frequencies to generate two signals each whose relative phases are ninety degrees apart.
It would be advantageous to have a circuit that generates two, high spectral purity, local oscillator carriers with a relative phase shift of ninety degrees that may be used in the modulation and demodulation process. It would be of further advantage for the circuit to be area and cost efficient.


REFERENCES:
patent: 5912596 (1999-06-01), Ghoshal
patent: 6456167 (2002-09-01), Huang

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