Amplifiers – With semiconductor amplifying device – Including differential amplifier
Reexamination Certificate
2002-06-04
2003-03-11
Nguyen, Patricia (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including differential amplifier
C330S260000, C327S359000
Reexamination Certificate
active
06531920
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to differential amplifiers and, more particularly, to a differential amplifier having a characteristic of low distortion even during low voltage operation and applicable for mixer circuits and variable gain amplifier circuits.
2. Description of the Prior Art
It is a known fact that in recent years, portable electronic equipment including portable telephones has been widely used in society. Also, it is well known that in radio systems to which portable electronic equipment is applied, in order to ensure a long calling time during battery-driven operation of the equipment, there have been demands for a reduction of the driving voltage of the portable electronic equipment, which is effective for reducing power consumption of the radio systems.
Further, it is well known that a differential amplifier circuit, a mixer circuit, and a variable gain amplifier circuit each are required to have a characteristic of low distortion to suppress an interference to an adjacent channel and deterioration in bit error rate caused by its inputting of disturbance waves.
However, the demands for lower supply voltage of portable equipment results in narrowing of its dynamic range for input/output signals, conflicting with the demands for lower distortion of the portable equipment. For this reason, it is very difficult to satisfy these two demands at the same time.
For these demands, a differential amplifier circuit improved in non-linearity (first conventional differential amplifier) is reported in a paper M. Koyama et. al., “A 2.5-V Active Low-Pass Filter Using All -n-p-n Gilbert Cells with a 1-V
p-p
Linear Input Range” (IEEE J. Solid State Circuits, Vol., SC-28, No. 12, pp. 1246-1253, Dec. 1993).
Further, a differential amplifier circuit (second conventional amplifier circuit) enabling the first conventional differential amplifier circuit to operate at low voltage is disclosed, for example, in Japanese Patent Laid-Open No. 8-250941.
Hereinafter, these conventional circuits will be described. First, the first conventional differential amplifier will be described.
FIG. 2
shows the first conventional differential amplifier circuit which is shown in the report “A 2.5-V Active Low-Pass Filter Using All -n-p-n Gilbert Cells with a 1-V
p-p
Linear Input Range”.
Referring to
FIG. 2
, the first conventional differential amplifier circuit comprises two input terminals
51
and
52
, two operational amplifiers
53
and
54
having the positive inputs connected to the input terminals
51
and
52
respectively, NPN transistors
71
and
72
having the bases connected to each output of the operational amplifiers
71
and
72
respectively, constant current sources
91
and
92
connected between each emitter of the transistors
71
and
72
, and a ground terminal
58
respectively, a feedback resistor
81
connected between the emitters of the transistors
71
and
72
, and load resistors
82
and
83
connected between each collector of the transistors
71
and
72
and a power supply terminal
57
respectively, wherein each emitter of the transistors
71
and
72
is connected to each negative input of the operational amplifiers
53
and
54
respectively, and each collector of the transistors
71
and
72
is connected to each of output terminals
61
and
62
respectively.
The first conventional differential amplifier circuit configured as described above operates as follows.
That is, in the first conventional differential amplifier circuit, a input voltage Vin inputted between a pair of the input terminals
51
and
52
is directly applied across the feedback resistor
81
through a pair of voltage follower circuits consisting of a set of the operational amplifier
53
and the transistor
71
and a set of the operational amplifier
54
and the transistor
72
. Herein, since the feedback resistor
81
is a linear element, a linear current flows through the resistor
81
according to a voltage applied across the resistor.
In the circuit of
FIG. 2
, the resistance value of the feedback resistor
81
is represented as RFB
1
and a signal current flowing through the feedback resistor
81
is represented as i. Then, the relation between RFB
1
and i can be expressed by the following equation.
i
=(
Vin/RFB
1
) (1)
A current given by the equation (1) flows through the respective emitters of the transistors
71
and
72
as a positive current and a negative current, respectively. Further, if the base currents flowing through the transistors
71
and
72
can be neglected because of the high current gain of the transistors, their emitter currents are equal to their collector currents. Therefore, the linear current given by the equation (1) is supplied through the load resistors
82
and
83
.
Herein, clearly from the equation (1), the transconductance Gm of the differential amplifier circuit of
FIG. 2
can be expressed by the following equation.
Gm
=(
i/Vin
)=(1
/RFB
1
) (2)
Further, the above respective collector currents are converted into the corresponding voltages through the load resistors
82
and
83
inserted between each collector of the transistors
71
and
72
and the power supply terminal
57
, and the resultant voltages are outputted to output terminals
61
and
62
.
By representing the resistance values of the load resistors
82
and
83
as RC, the voltage gain G of the differential amplifier circuit of
FIG. 2
can be expressed by the following equation, using equation (2).
G=Gm·Rc
=(
Rc/RFB
1
) (3)
On the other hand, when the current values of the constant current sources
91
and
92
each are represented as I
0
, the linear Input Dynamic Range (IDR) of the differential amplifier circuit of
FIG. 2
can be expressed by the following equation.
IDR=I
0
·
RFB
1
(4)
Also, the dc potential V
0
(DC) of the output terminals can be expressed by the following equation.
V
0
(
DC
)=
Vcc−I
0
·
Rc
(5)
As described above, the first conventional differential amplifier circuit can provide a linear output voltage according to an input voltage Vin without being affected by the non-linearity of the differential pair of the input transistors
71
and
72
.
FIG. 3
shows an example of the relations of input voltage (Vin) and transconductance (Gm) and output current (io, iob) for the first conventional differential amplifier circuit shown in FIG.
2
. In addition,
FIG. 3
also shows the relations of input voltage versus transconductance and output current for a most basic differential amplifier circuit with an emitter feedback resistor shown in FIG.
1
.
In the example of
FIG. 3
, the resistance value RFB
1
of the feedback resistor
81
is assumed to be 2000&OHgr; and the currents I
0
of the constant current sources
91
and
92
each are assumed to be 0.45 mA. It can be seen from
FIG. 3
that the first conventional differential amplifier circuit is superior in linearity to the differential amplifier circuit with an emitter feedback resistor shown in FIG.
1
.
The circuit diagram of
FIG. 4
shows a configuration of the first conventional differential amplifier circuit and the potential of each node therein. Herein, only a half of the circuit is shown because of the symmetry of the differential amplifier circuit.
Therein, the base of a transistor
531
, the base and the collector of a transistor
532
serve as a positive input, a negative input and an output of the operational amplifier
53
respectively, and the transistor
71
configures a voltage follower circuit. For this reason, when the potential of the input terminal
51
is represented as Vin, the base potential of the transistor
532
is also Vin, and therefore the base potential of the transistor
71
becomes (Vin+VBEQ
71
).
Next, the second conventional differential amplifier circuit will be described.
FIG. 5
shows the second conventional differential amplifier circuit shown in Japanese Patent Laid-Open No. 8-250941.
The second conventional differential a
Dickstein, Shapiro, Morin & Oshinsky L.L.P.
NEC Corporation
LandOfFree
Differential amplifier circuit does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Differential amplifier circuit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Differential amplifier circuit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3071761