Voltage control oscillator (VCO) with automatic gain control

Details Voltage control oscillator (VCO) with automatic gain control Voltage control oscillator (VCO) with automatic gain control

2000-07-18

2002-06-11

Mis, David (Department: 2817)

Oscillators

Ring oscillators

C331S010000

Reexamination Certificate

active

06404294

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method and/or architecture for a voltage controlled oscillator generally and, more particularly, to a method and/or architecture for an automatic gain control circuit for use with a voltage controlled oscillator.
BACKGROUND OF THE INVENTION
A voltage controlled oscillator (VCO) is commonly employed in a variety of applications, including communications, and timing circuitry. In particular, a VCO is commonly used in phase locked loop (PLL) control systems. Functionally, a VCO may be viewed as a circuit that seeks to transform an input control voltage signal into an output frequency signal in a substantially linear fashion. The frequency gain of a VCO typically defines the relationship between changes in the output frequency relative to predetermined changes in the input control voltage signal (i.e., delta frequency/delta voltage).
Referring to
FIG. 1
, a graph illustrating a linear frequency gain is shown. The linear relationship between the frequency of the signal FOUT and the magnitude of the voltage signal VIN may be expressed using the following equations:
ⅆ
f
ⅆ
v
=
m
∫
f0
f
n
⁢
ⅆ
f
=
m
⁢
 
⁢
∫
v0
v
n
⁢
ⅆ
v
f
n
=
m
(
v
n
−
v
0
)+
f
0
where m is the constant VCO gain, f0 and v0 are the initial values of the frequency of the signal FOUT, and fn and vn are the output frequency and the input voltage.
Referring to
FIG. 2
, a block diagram of a linear VCO
10
is shown. The VCO
10
includes an output stage
12
and an input stage
14
. The output stage
12
transforms a control current Ic into an output signal FOUT having a predetermined frequency based on the magnitude of the control current Ic. The input stage
14
converts an input voltage VIN into the control current Ic. For example, the output stage
12
can include a plurality of differential current switches connected in series with an output of a last current switch connected to an input of a first current switch (i.e., a so-called ring oscillator). The control current Ic is mirrored into the plurality of current switches controlling the output frequency (i.e., controlling the biasing current), or, alternatively, the magnitude of the control current is used to control a load associated with the plurality of current switches thereby varying the output frequency of the VCO.
The input stage
14
includes a transistor
16
and a transistor
18
. The signal VIN is presented to a gate of the transistor
16
. A resistor
20
couples a source of the transistor
16
to a voltage supply ground VSS. A drain of the transistor
16
is connected to a drain and a gate of the transistor
18
. A source of the transistor
18
is connected to a supply voltage VCC. A voltage across the resistor
20
varies in response to the signal VIN generating the control current Ic. The control current Ic is mirrored from the transistor
18
to the output stage
12
. Referring to
FIG. 3
, a schematic diagram illustrating a transistor implementation of the circuit
10
is shown.
Referring to
FIG. 4
, a graph illustrating the frequency gain for the circuit
10
is shown. The input stage
14
of a conventional VCO has a linear response—ostensibly in order to effect a linear VCO input/output response. The resistor
20
provides a constant VCO gain that can be used with a phase lock loop (PLL) for a stable control system that is not sensitive to change.
In certain applications, the linear gain of the VCO
10
may be a disadvantage. For example, a spread spectrum application can require a VCO with a nonlinear gain (i.e., a low gain at low frequencies and a high gain at high frequencies). A description of a spread spectrum application may be found in co-pending application U.S. Ser. No. 09/618,622, filed concurrently, which is hereby incorporated by reference in its entirety. Since the gain of the circuit
10
is controlled by the resistor
20
, the circuit
10
cannot achieve a nonlinear gain.
SUMMARY OF THE INVENTION
The present invention concerns an apparatus comprising a circuit configured to generate an output signal having a frequency that varies in response to a voltage signal, wherein said circuit has an automatically controlled nonlinear frequency gain.
The objects, features and advantages of the present invention include providing a method and/or architecture for automatic gain control in a voltage controlled oscillator (VCO) that may (i) provide an adaptive spread spectrum device, and/or (ii) provide a wider range of operating frequency than a conventional VCO.


REFERENCES:
patent: 5412349 (1995-05-01), Young et al.
patent: 5459653 (1995-10-01), Seto et al.
patent: 5748048 (1998-05-01), Moyal
patent: 5896068 (1999-04-01), Moyal
patent: 6005444 (1999-12-01), Carpelan

Affiliated with

Also associated with

Rating

Voltage control oscillator (VCO) with automatic gain control does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Voltage control oscillator (VCO) with automatic gain control, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Voltage control oscillator (VCO) with automatic gain control will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2909403