Method, circuit and/or architecture to improve the frequency...

Details Method, circuit and/or architecture to improve the frequency... Method, circuit and/or architecture to improve the frequency...

1999-06-08

2001-08-14

Kinkead, Arnold (Department: 2817)

Oscillators

Automatic frequency stabilization using a phase or frequency...

Particular frequency control means

C331S016000, C331S017000, C331S17700V

Reexamination Certificate

active

06275116

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to oscillators generally and, more particularly, to a method, circuit and/or architecture to improve the frequency range of a voltage controlled oscillator.
BACKGROUND OF THE INVENTION
Referring to
FIG. 1
, an example of a conventional phase locked loop circuit
10
is shown. The circuit
10
generally comprises phase frequency detector
12
, a charge pump
14
, a voltage controlled oscillator (VCO)
16
and a divider
18
. The circuit
10
is used to multiply a reference signal REFCLK having a fixed frequency, received at an input
24
, by some multiple set by the divider
18
. The frequency detector
12
is coupled to the VCO
16
through the charge pump/filter
14
. The divider circuit
18
has an input
28
that receives a feedback of the signal CLK presented at an output
30
of the VCO
16
. The divider
18
presents a signal to an input
32
of the frequency detector
12
. Errors coupled through the charge pump
14
cause the VCO
16
to change the frequency of the signal CLK to minimize the error. VCO frequency errors may be managed by the circuit
10
. The nominal frequency of operation of the signal CLK will be the frequency of the reference signal REFCLK multiplied by the divider ratio.
The VCO
16
is an integral part of the PLL
10
. The gain of the VCO
16
(i.e., the frequency of the signal CLK vs. the change in the input control voltage Vcontrol), and the frequency range of the VCO
16
are two very important design parameters. The gain of the VCO
16
is important to determine the bandwidth of the PLL
10
. Also, the gain of the VCO
16
has a significant impact on jitter (i.e., high frequency semi-random displacement of a signal from its ideal location). The frequency of the VCO
16
determines the operating frequency of the PLL
10
.
FIG. 2
illustrates a diagram of a conventional VCO
16
. The VCO
16
is usually made up of a voltage to current converter
40
and a current controlled oscillator (ICO)
50
. The converter
40
comprises a current mirror
42
, a comparator
44
, a transistor
46
and a resistor R. The frequency of operation of the VCO
16
is directly dependent on the current Ivco received by the ICO
50
. The current Ivco is the voltage of the signal Vcontrol divided by the resistance R. The higher the current IVCO, the higher frequency of the signal CLK. The current of the ICO
50
depends on the value of resistor R. Also, the gain of the VCO
16
depends on the value of the resistor R.
The value of the resistance R determines the gain of the VCO
16
(i.e., slope of the F-V curve). Changing the gain of the VCO
16
will also change the frequency of operation of VCO
16
. This may put the frequency of the VCO
16
out of the required range.
SUMMARY OF THE INVENTION
The present invention concerns a circuit comprising an oscillator configured to generate a periodic signal in response to (i) control signal and (ii) a current. The current may be varied independently of the control signal. In one example, the oscillator may generate the periodic signal in further response to a second current that may vary in response to the control signal. In another example, the oscillator may be used in a phase-locked loop circuit.
The objects, features and advantages of the present invention include providing an oscillator that may (i) generate a signal having a frequency that may be adjusted without changing the gain of the oscillator, (ii) have an expanded frequency range, (iii) provide an offset current to adjust the frequency, and/or (iv) provide post-production configuration of the oscillator.


REFERENCES:
patent: 5412349 (1995-05-01), Young et al.
patent: 6005444 (1999-12-01), Carpelan

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