Amplifiers – Sum and difference amplifiers
Reexamination Certificate
2001-05-16
2003-02-04
Pascal, Robert (Department: 2817)
Amplifiers
Sum and difference amplifiers
C341S131000
Reexamination Certificate
active
06515542
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to differential intermediate frequency amplifiers for driving analog to digital converting circuit or communication circuits. More specifically, the present invention is directed to differential intermediate frequency amplifiers including narrow band noise dithering for driving analog to digital converting circuit or communication circuits.
BACKGROUND OF THE INVENTION
Differential amplifiers have been widely used in communication applications due to their properties of even order harmonics cancellation and common mode noise rejection. An example of a conventional differential amplifier connected to a conventional analog to digital converting circuit is illustrated in FIG.
1
.
FIG. 1
shows a pair of operational amplifiers
112
and
160
configured in a non-inverting mode for intermediate frequency (“IF”) signals. Input signals are fed to the non-inverting inputs of the operational amplifiers
112
and
160
through resistors
106
and
152
, respectively. The non-inverting inputs of the operational amplifiers
112
and
160
are also connected to ground through a pair of resistors (
106
,
108
) and (
152
,
150
), respectively. The output of the pair of operational amplifiers
112
and
160
are fed back to their respective inverting inputs through resistors
110
and
158
, respectively.
The output of the operational amplifier
112
is fed to a non-inverting input of a differential in/out amplifier
120
through a resistor
114
and a capacitor
116
that are serially connected together. The output of the operational amplifier
160
is fed to an inverting input of differential in/out amplifier
120
through a resistor
162
and a capacitor
164
that are serially connected together.
The non-inverted output of the differential in/out amplifier
120
is fed to an input of an analog to digital converting circuit
140
through a resistor
126
and a capacitor
130
that are serially connected together. The inverted output of the differential in/out amplifier
120
is fed to an input of analog to digital converting circuit
140
through a resistor
124
and a capacitor
132
that are serially connected together. A capacitor
128
is connected across the center point of serially connected the resistor
126
and the capacitor
130
, and serially connected the resistor
124
and, the capacitor
132
. The non-inverted output of the differential in/out amplifier
120
is fed back to the inverted input of the differential in/out amplifier
120
through a resistor
118
. The inverted output of the differential in/out amplifier
120
is fed back to the non-inverted input of the differential in/out amplifier
120
through a resistor
122
.
Although differential amplifiers have been widely used to drive analog to digital converters and in communication applications, differential amplifiers only provide a limited spurious free dynamic range, thereby hindering optimization of these applications.
A conventional technique to improve a spurious free dynamic range is noise dithering. Noise dithering improves spurious free dynamic range of analog to digital converters by randomizing differential non-linearity of the analog to digital converter in its digitizing process.
However, such conventional dithering techniques have not been used with differential amplifiers because differential amplifiers have good common mode noise rejection, thereby making it difficult to combine or inject a dithering noise into the signal being amplified. Moreover, the injection of noise into a differential amplifier circuit can result in insertion loss and/or mismatching along the signal path.
It is desirable to enable a differential amplifier circuit that has the properties of even order harmonics cancellation and common mode noise rejection, as well as, an improved spurious free dynamic range.
SUMMARY OF THE INVENTION
One aspect of the present invention is directed to an amplifier circuit. The amplifier circuit includes an intermediate frequency signal circuit having an inverting input and a noise generating system connected to the inverting input of the intermediate frequency signal circuit.
Another aspect of the present invention is directed to an analog to digital conversion circuit. The analog to digital conversion circuit includes an intermediate frequency signal circuit having an inverting input; a noise generating system connected to the inverting input of the intermediate frequency signal circuit; and an analog to digital conversion circuit connected to the intermediate frequency signal circuit.
A third aspect of the present invention is directed to a method of amplifying an input signal. The method differentially amplifies an input signal using a differential amplifying circuit; feeds back an output signal of the differential amplifying circuit to an inverting input of the differential amplifying circuit; and injects a narrow band noise signal into the feedback signal being fed to an inverting input of the differential amplifying circuit.
REFERENCES:
patent: 5148163 (1992-09-01), Frindle
patent: 5451900 (1995-09-01), Haga et al.
patent: 6064328 (2000-05-01), Scheidig et al.
patent: 408249603 (1996-09-01), None
Hand James
Wang Yi
Analog Devices Inc.
Nguyen Khanh Van
Pascal Robert
Samuels , Gauthier & Stevens, LLP
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