Miscellaneous active electrical nonlinear devices – circuits – and – Specific input to output function – Combining of plural signals
Reexamination Certificate
1999-10-27
2001-06-12
Ton, My-Trang Nu (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific input to output function
Combining of plural signals
C327S306000
Reexamination Certificate
active
06246279
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to an output amplitude control circuit and, more particularly, to an output amplitude control circuit of a digital analog converting circuit that is appropriate for use in an arbitrary signal generator with which digital waveform data are applied to digital analog converters to generate analog signals.
BACKGROUND OF THE INVENTION
There are cases where it is necessary to adjust output amplitude without changing the iput digital waveform data in arbitrary signal generators (AWGs) and audio signal sources, etc., with which digital waveform data are input to a digital analog converter (D-A converter; DAC) and analog signals are generated.
FIG. 1
is a conventional circuit with which fixed resistor
102
and relay
103
are connected to the output of a D-A converter (not illustrated) via analog input
101
, and the relay switch is switched and controlled by relay control circuit
106
in order to adjust the amplitude of analog output. The desired amplitude is obtained from analog output
104
based on the combination in which the relay switches are connected and disconnected. However, there is a problem with this structure in that it is necessary to use high-precision resistors and therefore, its cost is high. Moreover, many resistors and relays are needed for precise control of resolution and therefore, there are limits to the capability of such a system. Furthermore, there is a disadvantage in that because operating speed of the relays is slow, high-speed amplitude control is not possible. In addition, there is a problem in that the parts are large and miniaturization of the circuit is impossible.
FIG. 2
is another conventional circuit which, using a digital filter as digital multipiler
202
, the amplitude of the analog output of D-A converts is adjusted by multiplying a proportional coefficient by the input digital signals and inputting to D-A converter
201
. However, by means of this structure, there is a problem since there are limits to the operating speed of the digital multiplier, and high-speed operation is impossible.
FIG. 3
is yet another conventional circuit that uses D-A converter (multiplying-type DAC)
301
with which the reference voltage for D-A conversion can be adjusted to generate reference voltage Vref by D-A converter
302
and add it to D-A converter
301
. However, there is a problem in that when this type of structure is used, D-A converter
301
that can use reference voltage is necessary and reference voltage Vref is an analog value and noise can easily increase. Inserting an analog filter between D-A converter
301
and D-A converter
302
has been considered to prevent this noise from being generated, but there is a disadvantage in this case in that high-speed control of DAC output amplitude is not possible.
SUMMARY OF THE INVENTION
The present invention eliminates the disadvantages of the abovementioned prior art, its purpose being to present an amplitude control circuit wherein parts that slow operating speed, such as relays, digital multipliers, analog filters, etc., are omitted and high-speed operation is therefore possible. Another purpose is to easily produce a high-precision amplitude control circuit wherein the effects of changes attributed to part precision and drift that occur with analog circuits can be eliminated by adjusting the signal amplitude using a digital circuit. Yet another purpose is to eliminate the necessity of using many high-precision parts, particularly high-precision resistors, and to make possible the use of D-A converters that are not multiplying converters, particularly D-A converters that are marketed for audio use, and thereby reduce cost.
In short, the present invention (1) is characterized in that it is an output amplitude control circuit of a digital analog converting circuit with the following structure:
(1) a multiple nimber of digital analog converters
(2) an input signal converting circuit that receives input digital signals and outs a first digital signal and a second digital signal that have a specific relationship with said input digital signals and have different values
(3) a multiple number of switches that connect with each of the digital analog converters that selectively apply the first digital or second digital signal to the digital analog converters
(4) an adder that adds the output of the multiple number of digital analog converters
(5) a means whereby the analog output amplitude is adjusted by changing the ratio of selection of the first digital signal or second digital signal by the nmltiple number of switches
In addition, the present invention (2) is characterized in that it is an output amplitude control circuit of a digital analog converting circuit with the following structure:
(1) a multiple number of digital analog converters
(2) an input signal converting circuit that receives input digital signals and outputs a first digital signal and a second digital signal that have a specific relationship with said input digital signals and have different values
(3) a multiple number of switches that connect with each of the digital analog converters that selectively apply the first digital or second digital signal to said digital analog converters
(4) an adder that adds the output of the multiple number of digital analog converters
(5) an attenuator connected to said adder output that can establish a multiple number of attenuated fixed values
(6) a means whereby the amplitude is controlled to less than the resolution of the attenuated fixed value that can be established by the attenuator by changing the ratio of selection of the first and second digital signals by the multiple number of switches
Moreover, the present invention (3) is characterized in that, in the present invention (1) or (2), the input signal converting circuit allows the input digital signals to pass through as the first digital signal, while it performs a specific type of operation on the input digital signals to obtain the second digital signal
Moreover, the present invention (4) is characterized in that a slightly smaller value than the value of the input digital signals is obtained by the specific type of operation in present invention (3).
Moreover, the present invention (5) is characterized in that operation to obtain a slightly smaller value than the value of the input digital signals in present invention (4) is: ((nth power of 2)—1)/(nth power of 2)).
Moreover, the present invention (6) is characterized in that the circuit that performs the operation of ((nth power of 2)—1)/(nth power of 2) in present invention (5) comprises a shift register connected to the input, a sign inversion circuit connected to the output of said shift register, and an adder that adds said sign inversion circuit output and the input signals from the input.
Moreover, the present invention (7) is characterized in that the value of n is 4 and the number of digital analog converters and switches is 6 each in present invention (5) or (6).
Moreover, the present invention (8) is characterized in that the input digital signals are parallel signals, the digital analog converters are serial signal input-type converters, and a parallel-serial converter is connected to the first digital signal output and second digital signal output of the input signal converting circuit in present inventions (1) through (8).
Moreover, the present invention (10) is characterized in that switch control circuits that receive amplitude control signals and control each switch are connected to the switches in present inventions (1) through (9).
Moreover, the present invention (11) is characterized in that it is an output amplitude control circuit of a digital analog converting circuit with the following structure:
(1) a multiple number of digital analog converters
(2) an input signal converting circuit that receives input digital signals and outputs a multiple number of intermediate digital signals that have a specific relationship with said input digital signals and have different values
(3) a multiple number of switches that con
Agilent Technologies
Nu Ton My-Trang
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