Voltage controlled oscillator (VCO) in colpitts configuration

Details Voltage controlled oscillator (VCO) in colpitts configuration Voltage controlled oscillator (VCO) in colpitts configuration

2001-01-03

2002-10-15

Kinkead, Arnold (Department: 2817)

Oscillators

Solid state active element oscillator

Transistors

C331S17700V, C331S03600C, C331S179000

Reexamination Certificate

active

06466099

ABSTRACT:

FIELD OF THE INVENTIONA
The present invention generally relates to a voltage controlled oscillator (VCO), and, more particularly, to a VCO in Colpitts and/or Clapp configuration with varactors.
BACKGROUND OF THE INVENTION
Voltage controlled oscillators (VCO) are designed to produce an oscillating signal (“carrier signal”) of a particular frequency F. Typically, VCOs are used in radio receiver and transmitter circuits. VCOs often comprise tank circuits with inductors as well as with variable capacitors. These capacitors are usually implemented by varactor diodes (in short “varactors” or “varicap”).
The frequency F of the oscillating signal is determined by the magnitude of a tuning voltage V
TUNE
applied to the varactor (to its pn-junction). The frequency F can be varied reliably between a certain maximum frequency F
MAX
and a certain minimum frequency F
MIN
, often a radio frequency (RF). The frequencies between these limits are referred to as the VCO's frequency range (or “bandwidth”). The VCO tuning sensitivity is defined as frequency change over tuning voltage change (i.e. derivation dF/dV
TUNE
). It is desired to tune the oscillator over a large frequency range with a small tuning voltage range.
However, there are also particular requirements for low noise performance over the complete frequency range. Noise that appears around the oscillator frequency can lead to unwanted phase or frequency modulation of the oscillating signal; this so-called phase noise is a relative power usually measured in a 1 Hz bandwidth, at a measurement frequency that is offset (e.g., 25 kHz) to the frequency F of the oscillating signal (single side-band phase noise), the unit is “dBc in 1 Hz”.
Resistive losses especially those in the inductors and varactors are of major importance and determine the quality factor Q of each tank circuit; generally, a high Q is desirable. With the desire to provide small VCOs (e.g., in portable radios), the achievable Q decreases, thus leading to further unwanted effects such as higher noise and a small frequency range.
Since each VCO needs an amplifying element combined with a feedback network, the open loop gain of that arrangement might vary (i.e. increase) with the frequency. Also, quality factor Q variations might cause an unwanted signal level change of the tank circuit that further influences the performance of the VCO.
Both such gain and Q variations might lead to an unwanted increase of the oscillating signal amplitude at higher frequencies; this needs to be accommodated, for example, by regulating means.
Also, with increasing frequency range, the noise might be more frequency dependent, the power consumption might rise, and the output power might fall. In other words, the overall performance is optimal for few frequencies only.
The following references are useful: U.S. Pat. No. 1,624,537 (Colpitts); U.S. Pat. No. 2,756,334 (Blum); U.S. Pat. No. 2,225,897 (Bell); U.S. Pat. No. 4,621,241 (Kiser); U.S. Pat. No. 4,785,263 (Kaltenecker et al.); U.S. Pat. No. 5,144,264 (Chong et al.), U.S. Pat. No. 5,959,504 (Wang); U.S. Pat. No. 5,982,243 (Pope), U.S. Pat. No. 6,046,647 (Nelson); U.S. Pat. No. 6,081,167 (Kromat); as well as WO99/53608 (Lichterfeld).
There is a need to find a simple VCO that allows a good compromise between performance and limited space.


REFERENCES:
patent: 1624537 (1927-04-01), Colpitts
patent: 2225897 (1940-12-01), Bell
patent: 2756334 (1956-07-01), Blum
patent: 4621241 (1986-11-01), Kiser
patent: 4785263 (1988-11-01), Kaltenecker et al.
patent: 5144264 (1992-09-01), Chong et al.
patent: 5469117 (1995-11-01), Philippe
patent: 5959504 (1999-09-01), Wang
patent: 5982243 (1999-11-01), Pope
patent: 6046647 (2000-04-01), Nelson
patent: 6081167 (2000-06-01), Kromat
patent: WO 99/53608 (1999-10-01), None

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