Differential type voltage controlled oscillator

Details Differential type voltage controlled oscillator Differential type voltage controlled oscillator

2002-03-18

2003-09-16

Dinh, Son T. (Department: 2824)

Oscillators

Solid state active element oscillator

Transistors

C331S1170FE, C331S034000, C331S17700V

Reexamination Certificate

active

06621363

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention The present invention relates to a voltage controlled oscillator (VCO) using a differential amplifier, and more particularly to a VCO using LC oscillator and a differential oscillator. The present application is based on Korean Application No. 2001-72471, which is incorporated herein by reference.
2. Description of the Related Art
FIG. 1
is a circuit diagram of a conventional VCO. It utilizes a differential amplifier and an LC tank(oscillator).
Referring to
FIG. 1
, a differential amplifier includes a couple of MOSFETs
10
and
12
for embodying a negative resistance, and another MOSFET
36
for embodying a current source controlling the MOSFETs
10
and
12
. An LC tank includes variable capacitors
26
and
28
and inductors
14
and
20
which are connected to a drain port of each MOSFET
10
and
12
. A current source
36
is controlled by a voltage applied to an input node
38
. Variable capacitors
26
and
28
are controlled by a control voltage of a control node
34
.
From a view from the LC tank, there is formed an impedance of a negative resistance on the differential amplifier, and consequently an output signal is generated from nodes
30
and
32
each connected to the drain of each MOSFET
10
and
12
. The output signal generated from the nodes
30
and
32
is output at output nodes
18
and
24
through buffers
40
and
42
which include transistors.
However, as above described, in the conventional differential VCO, the buffer must be provided to pass the launch signal from the LC tank to other circuits, which results in much greater power consumption. That is, as shown in
FIG. 1
, since buffers
40
and
42
include transistors which consume additional power in addition to that consumed in each MOSFET embodying a negative resistance, much power is consumed.
Generally, it is very important to reduce power consumption in RF systems which use an oscillator and there are various methods for reducing the power consumption in the differential amplifier corresponding to a core portion of the oscillator. However, even if the power consumption in the differential amplifier decreases, the overall decrease in power consumption is limited since buffers
40
and
42
consume power continuously.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the above described problem of conventional methods and therefore to provide a VCO using an LC tank and a differential amplifier which reduces power consumption in a buffer portion.
To achieve the above objects of the invention, there is provided a differential type voltage controlled oscillator comprising:
a current source;
a differential amplifier having a couple of transistors amplifying a difference of input signals controlled by the current source;
a couple of LC tanks oscillating an output signal from the transistors so as to generate the input signals; and
a couple of transformers utilizing an inductor of each LC tank as a primary coil and generating an oscillating output signal from a secondary coil thereof.
According to a preferred embodiment of the invention, there is also provided a capacitor connected in parallel or in series with the secondary coil of the transformer so as to remove a harmonic signal contained in the oscillating output signal.
The oscillating signal is output through the transformer (buffer) so that it does not consume additional power.


REFERENCES:
patent: 5818306 (1998-10-01), Lee et al.
patent: 6016082 (2000-01-01), Cruz et al.
patent: 6150893 (2000-11-01), Fattaruso
patent: 6249190 (2001-06-01), Rozenblit et al.
patent: 6268778 (2001-07-01), Mucke et al.
patent: 6469585 (2002-10-01), Dai et al.
patent: 6469587 (2002-10-01), Scoggins

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