Low impedance clamping buffer for an LC tank VCO

Details Low impedance clamping buffer for an LC tank VCO Low impedance clamping buffer for an LC tank VCO

2000-09-29

2002-03-26

Kinkead, Arnold (Department: 2817)

Oscillators

Solid state active element oscillator

Transistors

C331S034000, C331S167000, C331S1170FE, C331S185000, C330S098000, C330S310000

Reexamination Certificate

active

06362698

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally concerns phase locked loops (PLLs), and in particular concerns conditioning circuitry for use with PLLs that employ LC tank voltage-controlled oscillators.
2. Background Information
Phase locked loop (PLL) circuits are used to provide precise control of a frequency output signal in many types of electronic devices. A PLL circuit
10
corresponding to a typical PLL is shown in FIG.
1
. PLL circuit
10
employs a closed feedback loop comprising a phase detector
12
, a charge pump
14
, a loop filter
16
, and an oscillator, such as voltage-controlled oscillator (VCO)
18
or a current-controlled oscillator (ICO) (not shown). PLLs may also include a frequency divider
22
in the feedback portion of the loop. Ideally, a PLL will produce an output signal
20
(F
out
) having a frequency that matches a reference frequency control signal
24
(F
ref
).
Phase locked loops work in the following manner. The frequencies of output signal
20
(the loop feedback signal) and frequency control signal
24
are compared by phase detector
12
, which outputs a pair of digital control signals
26
and
28
to charge pump
14
. It will be understood by those skilled in the art that various types of phase detectors may be used, including phase detectors that output other types of control signals. The control signals selectively activate the current sources in charge pump
14
to control the voltage level of an unfiltered signal
30
, which is then filtered by the passive elements (i.e., capacitors C
2
and C
3
and resister R
2
) of loop filter
16
to produce a filtered VCO control signal
32
. This control signal drives VCO
18
, which produces output signal
20
, wherein the frequency of output signal
20
is a direct function of the voltage level of filtered VCO control signal
32
. In many instances, the frequency characteristic of the various circuit components will be such that it will be preferable to employ frequency divider
22
, e.g., when the desired frequency is >1 MHz.
The characteristics of VCO
18
are very important to the performance of the PLL. Preferably, VCO
18
should be resistant to power supply and ground noise, coupling of spurious frequencies from nearby devices, have minimized jitter, and be able to provide a large variable frequency output based on a small variation in the voltage level of its input control signal.


REFERENCES:
patent: 5739729 (1998-04-01), Tchamov et al.

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