Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Unwanted signal suppression
Reexamination Certificate
2002-04-02
2003-03-25
Le, Dinh T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Unwanted signal suppression
C327S552000
Reexamination Certificate
active
06538498
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gm-C tuning circuit and method for using same, and in particular to a gm-C tuning circuit using a poly-phase filter.
2. Background of the Related Art
Generally, a post-fabrication transconductance of an operational transconductance amplifier (OTA) should be adjusted according to the process-variations of components to maintain a selected precise cut-off frequency. A gm-C tuning scheme generally uses a master-slave tuning scheme to adjust a filter frequency that is inversely proportional to gm/C time constant (or RC time constant). In the master-slave tuning scheme, a master circuit is a copy of a slave block. The master circuit receives absolute frequency information from an external oscillator and adjusts transconductance to get the selected filter cut-off frequency. The control voltage of a master tuning feedback loop in the master circuit is copied to the slave block to reproduce the adjusted transconductance on the slave block. Then, the slave block becomes a main filter body whose cut-off frequency is controlled by the master circuit. Three related art master-slave tuning circuits will now be described.
FIG. 1
is a diagram that illustrates a master-slave voltage controlled oscillator (VCO) based tuning scheme. As shown in
FIG. 1
, a master block
110
outputs a control voltage
130
to a slave filter
140
. As shown in
FIG. 1
, the master circuit
110
includes a comparator
111
, a low pass filter
112
, a rectifier
113
, a voltage-to-current (V-I) converter
115
, a low pass filter
116
that outputs a feedback signal
118
and a master VCO
120
. The slave filter
130
is a copy of a master circuit.
In the master circuit
110
, a comparator
111
compares a reference frequency Fref with an output frequency of the master VCO
120
f
m
. The low pass filter
112
low pass filters an output of the comparator to provide the control voltage
130
of the master circuit
110
that is copied to the slave filter
130
. The rectifier
113
rectifies the output frequency f
m
from the master VCO
120
, and the V-I converter
115
converts an input voltage from the rectifier
113
and a reference voltage Vref The low pass filter
116
receives a converted current from the V-I converter
115
and outputs the feedback signal
118
to the master VCO
120
. In
FIG. 1
, an oscillation frequency of the master VCO
120
is determined by a time constant of each integrator, that is, the C/gm time constant when the gm-C integrator is used for the master VCO
120
. The gm-C VCO based tuning circuit has relatively small hardware requirements and a simple feedback structure. However, the related art gm-C VCO tuning circuit has the disadvantage that a very high Q-factor is required for the VCO oscillation.
FIG. 2
is a diagram that illustrates another related art master-slave voltage controlled filter tuning scheme. As shown in
FIG. 2
, a master block
210
includes a comparator
211
, a low pass filter
212
, first and second rectifiers
213
,
214
, a voltage to current (V-I) converter
215
, a low pass filter
216
and a master biquad
220
. The master block
210
copies a control voltage
230
to a slave filter
240
. The master circuit
210
is a copy of a slave filter
240
.
As shown in
FIG. 2
, the comparator
211
of the master block
210
receives a reference voltage Fref frequency and an output frequency f
m
from the master biquad. The low pass filter
212
receives an output from the comparator
211
and outputs the control voltage
230
to the slave filter
240
and the master biquad
220
. The first rectifier
213
receives the output frequency f
m
from the master biquad
220
, and the second rectifier
214
receives the reference frequency Fref. The V-I converter
215
receives an output from the first rectifier
213
and the second rectifier
214
, respectively. The low pass filter
216
receives an output from the V-I converter
215
and provides a second feedback signal to the master biquad
220
. In the related art master-slave voltage controlled filter tuning circuit shown in
FIG. 2
, the quality factor of the filter is used for the feedback loop control signal
218
. However, to provide sufficient sensitivity for phase tuning, the quality factor of the master circuit
210
must be large enough to provide sufficient sensitivity to phase tuning. The large quality factor of the master circuit
210
results in poor matching between the master block
210
and the slave block
240
, which determines accuracy of the master-slave tuning system. The quality factor, Q, of the filter is used for the feedback loop control signal
218
is shown at equations 1A, 1B, 2A and 2B as follows:
H
(
s
)
L
P
F
=
ϖ
0
2
s
2
+
(
ϖ
0
/
Q
)
s
+
ϖ
0
2
(1A)
H
(
s
)
B
P
F
=
ϖ
0
s
s
2
+
(
ϖ
0
/
Q
)
s
+
ϖ
0
2
(1B)
wherein H
LPH
of Equation 1A and H
BPF
of Equation 1B are the Laplace transforms of the low pass filter and the band pass filter, respectively, of FIG.
2
. Substituting the j{tilde over (&ohgr;)} for the Laplace variable s yields.
H
(
jϖ
0
)
L
P
F
=
ϖ
0
2
-
ϖ
0
2
+
(
ϖ
0
/
Q
)
jϖ
0
+
ϖ
0
2
=
-
j
Q
(2A)
H
(
jϖ
0
)
B
P
F
=
jϖ
0
2
-
ϖ
0
2
+
(
ϖ
0
/
Q
)
jϖ
0
+
ϖ
0
2
=
Q
(2B)
FIG. 3
is a diagram that illustrates a related master-slave single integrator tuning scheme. As shown in
FIG. 3
, a master block
310
copies control voltage
330
to a slave filter
340
. The master block
310
is a copy of the slave filter
330
. As shown in
FIG. 3
, the master block
310
includes a first rectifier
313
, a second rectifier
314
, a voltage to current (V-I) converter
315
, a low pass filter
316
and a single integrator
320
. As shown in
FIG. 3
, the first rectifier
313
receives an output frequency f
m
from the single integrator
320
, and the second rectifier
314
receives a reference frequency Fref. The V-I converter
315
receives output signals from the first rectifier
313
and the second rectifier
314
. The low pass filter
316
receives output from the V-I converter
315
to output the control voltage
330
to the slave filter
340
and as a feedback signal
318
to the single integrator
320
.
As shown in
FIG. 3
, the related art master-slave single integrator tuning scheme uses gm-C integrator
320
as the master of tuning to overcome various problems associated with the VCO type tuning scheme and the VCF type tuning scheme described above. In the single integrator tuning scheme shown in
FIG. 3
, the gm-C integrator
320
operates as a capacitor equivalent. The amplitude of the gm-C integrator
320
output and that of the input Fref are compared using the rectifier
313
,
314
and the V-I converter
315
. However, the input of the gm-C integrator
320
comes from an external oscillator and an output comes from an Operational Transconductance Amplifier (OTA) cell, which causes inaccurate tuning results.
In all of the above-discussed related art approaches, either a high Q factor results in poor matching between the master and the slave, or the input of gm-C integrator comes from an external oscillator and the output comes from the OTA cell which produces inaccurate timing results.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.
SUMMARY OF THE INVENTION
An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.
Another object of the present invention is to provide a master-slave circuit not limited by frequency or Q-factor requirements.
Another object of the present invention is to provide a master-slave tuning circuit using a poly-phase filter
Jeong Deog-Kyoon
Lee Kyeongho
Fleshner & Kim LLP
GCT Semiconductor Inc.
Le Dinh T.
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