Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Converting input voltage to output current or vice versa
Reexamination Certificate
1999-11-12
2001-12-11
Kim, Jung Ho (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Converting input voltage to output current or vice versa
C327S323000
Reexamination Certificate
active
06329849
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to apparatus and method for converting differential input voltage to fully balanced output currents.
More particularly, the present invention relates to an apparatus and method for converting differential input voltage to fully balanced output currents by adding/duplicating an output section of an operational transconductance amplifier.
2. Discussion of the Background
Furthermore, the present invention relates to an apparatus and method for controlling common mode component of two output currents by using a simplified common mode controlling circuit.
As an input differential voltage/output currents converter, an operational transconductance amplifier (hereinafter referred to as an “OTA”) has been developed for converting input differential voltage V
1
−V
2
into two output currents I
O1
, I
O2
, which are assumed to be balanced around a fixed constant value of a reference current I
REFCM
. In the simplest version of the OTA that can convert the input differential voltage into two fully balanced output currents I
o1
, I
o2
(hereinafter referred as a “FB-OTA”) the value of a reference current I
REFCM
is assumed to be zero. Usually, such a FB-OTA includes load circuits which are coupled to the output terminals of the OTA, respectively. In general, each of load circuits has the same impedance.
Typically, when differential input voltage V
1
−V
2
is applied to the OTA, the converted output currents I
O1
, I
O2
inevitably include common mode component due to influences of outside noises during conversion in the OTA. In particular, when the OTA, which is a part of analog system, is integrated with digital systems together on the same substrate, the converted output currents include common mode component due to noises which are generated from the digital circuits. Consequently, it has been need to take some measurements for eliminating such undesired common mode components at the output currents to make the available amplitude of a differential output voltage as large as possible.
Conventionally, a common mode control circuit has been proposed to apply to the OTA for generating a common mode feedback control signal or a common mode feedforward control signal to the OTA. The former type OTA is called as a common mode feedback controlled type OTA (hereinafter referred to as a “CMFB”-OTA). The latter type OTA is called as a common mode feedforward controlled type OTA (hereinafter referred to as a “CMFF”-OTA)
FIGS. 14-18
are related to a conventional common mode feedback controlled type fully balanced OTA implementations.
FIG. 19
shows an example of a common mode feedforward controlled type fully balanced OTA implementation.
In
FIG. 14
, the CMFB-OTA includes an OTA (
1
) for converting differential input voltage V
1
−V
2
to two output currents I
O1
, I
O2.
and a CMFB circuit (
2
a
) for generating common mode feedback control voltage V
B
to the OTA (
1
). The output terminals of the OTA(
1
) are coupled to load circuits (
3
a
), (
3
b
), respectively.
When the OTA(
1
) converts the differential input voltage V
1
V
2
into two output currents I
O1
, I
O2
, available from the output terminals of the OTA(
1
), the output voltages V
O1
, V
O2
are produced in accordance with a respective impedance of the load circuits (
3
a
), (
3
b
). The CMFB circuit (
2
a
) generates a feedback control voltage V
B
, which is a function of output voltages V
O1
, V
O2
, for strong suppression/elimination of a common mode component in the output currents I
o1
, I
o2
.
FIG. 15
shows a conventional circuit of the OTA (
1
). The OTA (
1
) is comprised of four PMOS transistors (Q
101
)-(Q
104
), two NMOS transistors (Q
105
), (Q
106
), four constant-current sources (
101
)-(
104
) and a resistor (R
1
). The input voltages V
1
, V
2
are respectively applied to each of the gate terminals of the NMOS transistors (Q
105
) and (Q
106
). The CMFB circuit (
2
a
) supplies a control voltage V
B
to a commonly coupled gate terminals of the two PMOS transistors (Q
101
) and (Q
102
) in the OTA(
1
). A predetermined voltage V
BO
is applied to the respective gate terminals of the another two PMOS transistors (Q
103
) and (Q
104
). From the respective drain terminals of these two PMOS transistors (Q
103
) and (Q
104
), output currents I
O1
, I
O2
, are available, respectively. The differential output voltage V
O1
−V
O2
is produced in accordance with the impedance for each of the load circuit (
3
a
) and (
3
b
).
FIG. 16
shows a conventional CMFB circuit (
2
a
). The circuit construction has been disclosed in a publication, IEEE Journal of Solid State Circuits, Vol.23, No.6, pp.1410-1414, December 1988 as in the tile of “Fully Differential Operational Amplifiers with Accurate Output balancing” by M. Banu, J. M. Khoury and Y. Tsividis.
In
FIG. 16
, the CMFB circuit (
2
a
) is comprised of a buffer circuit (
110
), a voltage divider (
111
) and a sense amplifier (
112
). The buffer circuit (
110
) is comprised of two operational amplifier (OP
1
), (OP
2
). The voltage divider (
111
) is comprised of two resistors (R
2
), (R
3
) and two capacitors (C
1
), (C
2
). The sense amplifier (
112
) is constructed with two PMOS transistors (Q
111
), (Q
112
), two NMOS transistors (Q
113
), (Q
114
) and a constant-current source (
113
). The output voltages V
O1
, V
O2
from the OTA (
1
) are applied to the buffer circuit (
110
). It is required, the input impedance of a buffer circuit to be as large as possible. Assuming a very high gain of OP
1
and OP
2
, the gain of the buffer circuits become very closed to one.
When both of the two resistors (R
2
) and (R
3
) have the same resistance value and also both of the two capacitors (C
1
) and (C
2
) has the same capacitance value, a control voltage V
Csens
at the output of the voltage divider (
111
) is expressed by the following equation (1).
V
Csens
=(
V
O1
+V
O2
)/2=
V
cm
(1a)
The voltage V
cm
is named as a common mode output voltage. The differential mode output voltage is defined as follows
V
dm
=(
V
O1
−V
O2
)/2 (1b)
According to (
1
a
) and (
1
b
) the output voltages V
O1
, and V
O2
can be respectively expressed as follows.
V
O1
=V
dm
+V
cm
,
V
O2
=−V
dm
+V
cm
The main function of a FB-OTA is suppression, or more precisely elimination in an ideal case, of a common mode component V
cm
at V
o1
and V
o2
.
The sense amplifier (
112
) in the CMFB circuit (
2
a
) compares the output voltage V
C
=V
cm
from the voltage divider (
111
) and a reference voltage V
ref
that is applied from the outside. The sense amplifier (
112
) provides a control voltage V
B
to OTA shown in
FIG. 14
for which a common mode component at the OTA output voltages V
o1
, V
o2
is strongly suppressing (eliminating in an ideal case). Practically, the common mode voltage V
cm
is eliminated with respect to the reference voltage V
ref
by using the feedback output from the CMFB circuit. However, as depicted in
FIG. 16
, the conventional CMFB circuit (
2
a
) must be comprised of two operational amplifiers (OP
1
) and (OP
2
). Further the CMFB circuit (
2
a
) must include the sense amplifier (
112
). This configuration arises many of serious problems for making the voltage/current converter in a small sized compact form and with limited amount of a power consumption.
Another type of the CMFB circuit (
2
a
), which allows a power consumption to be limited, is shown in FIG.
17
. This circuit configuration has been disclosed in a publication “CMOS Circuit Design, Layout and Simulation” by R. J. Baker, H. W. Li and D. E. Boyce.
The CMFB circuit (
2
a
) construction shown in
FIG. 17
includes a first sense differential pair (
121
) for comparing an input voltage V
01
with a reference voltage V
ref
and a second sense differential pair (
122
) for comparing an input V
O2
with the reference voltage V
ref
. A control voltage V
B
is produced by summing up the results of the first and second sense diff
Czarnul Zdzislaw
Ishii Hirotomo
Oda Kazuhiro
Kabushiki Kaisha Toshiba
Kim Jung Ho
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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