Analog-to-digital conversion device

Details Analog-to-digital conversion device Analog-to-digital conversion device

2000-03-09

2001-10-02

Williams, Howard L. (Department: 2819)

Coded data generation or conversion

Converter compensation

C341S155000

Reexamination Certificate

active

06297756

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an analog-to-digital (hereinafter also “A/D”) conversion device that converts an analog signal fed thereto into a digital signal and outputs the digital signal, and more particularly to an A/D conversion device having an input level adjustment function for adjusting the DC (direct-current) level of the analog signal fed thereto.
2. Description of the Prior Art
In analog-to-digital conversion, a fluctuation in the DC level of an input analog signal causes a distortion in the digital signal obtained as a result of analog-to-digital conversion. This is because analog-to-digital conversion can cope with a limited range of voltages.
To prevent such distortion, some A/D conversion devices are provided with an input level adjustment function for adjusting the DC level of the analog signal that is to be subjected to analog-to-digital conversion. The circuit configuration of a conventional A/D conversion device having such an input level adjustment function is shown in FIG.
3
. As shown in
FIG. 3
, this A/D conversion device is composed of an operational amplifier
1
, resistors
2
and
3
, an A/D converter that performs A/D conversion on a signal fed thereto and outputs the resulting signal, and a variable constant voltage source
50
that produces a constant voltage that can be varied.
To the non-inverting input terminal (+) of the operational amplifier
1
, an analog signal fed in via a signal input terminal T
1
is fed. On the other hand, the inverting input terminal (−) of the operational amplifier
1
is connected through the resistor
2
to the output terminal of the operational amplifier
1
itself, and is connected also through the resistor
3
to the variable constant voltage source
50
. The signal output from the operational amplifier
1
is subjected to A/D conversion by the A/D converter
4
, and is then output via terminals T
O1
, T
O2
, . . . , T
On
.
With respect to the operational amplifier
1
, negative feedback is achieved through the resistor
2
. Accordingly, if it is assumed that the voltage fed in via the terminal T
I
is V
I
, the resistances of the resistors
2
and
3
are R
f
and R respectively, and the constant voltage output from the variable constant voltage source
50
is V
B
, then the voltage V
A
of the analog signal fed to the A/D converter
4
is given by
V
A
={(R
f
+R)/R}V
I
−(R
f
/R)V
B
Accordingly, by adjusting the constant voltage V
B
of the variable constant voltage source
50
, it is possible to adjust the DC level of the analog signal fed to the A/D converter
4
. In this way, even if a fluctuation occurs in the DC level of the analog signal that is fed in via the terminal T
I
so as to be subjected to A/D conversion, or even if an offset occurs in the output of the operational amplifier
1
, it is possible to prevent the output digital signal from being distorted.
However, in this conventional A/D conversion device, to vary the DC level of the voltage V
A
of the analog signal fed to the A/D converter
4
by &Dgr;V
A
, the constant voltage V
B
of the variable constant voltage source
50
needs to be varied by &Dgr;V
B
, which is given by
&Dgr;V
B
=−(R/R
f
)×&agr;V
A
Thus, depending on the values at which the resistances R
f
and R are actually set, the voltage V
B
of the variable constant voltage source
50
needs to be adjusted within an extremely narrow range (more specifically, the farther R
f
is higher than R, the narrower the range of adjustment), which makes the adjustment of the voltage V
B
of the variable constant voltage source
50
extremely difficult.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an analog-to-digital conversion device having an input level adjustment function that allows adjustments needed to prevent the output digital signal from being distorted to be made with more ease.
To achieve the above object, according to one aspect of the present invention, an A/D conversion device having an input level adjustment function that converts an analog signal fed thereto into a digital signal to be output and that allows adjustment of the DC level of the analog signal fed thereto to be converted into a digital signal is composed of a terminal for receiving a voltage from the outside, a voltage division circuit for dividing the voltage difference between the voltage received at the terminal and an internal constant voltage, a buffer amplifier that receives the voltage resulting from voltage division performed by the voltage division circuit, an amplifier that receives the analog signal to be converted and that has a negative feedback circuit that uses as a reference voltage the voltage output from the buffer amplifier, and an A/D converter for converting the signal output from this amplifier into a digital signal.
According to this circuit configuration, by adjusting the voltage fed in from the outside, it is possible to vary the DC level of the analog signal fed to the A/D circuit. Moreover, a given change in the DC level can be achieved by adjusting the voltage in a wider range than ever.
According to another aspect of the present invention, an analog-to-digital conversion device is provided with: a signal input terminal for receiving an analog signal; a direct-current voltage source whose output voltage can be varied; a direct-current voltage input terminal for receiving a direct-current voltage output from the direct-current voltage source; a first resistor, a second resistor, and a constant voltage source connected in series in this order from the direct-current voltage input terminal; an amplifier having an input terminal connected to the node between the first and second resistors; an operational amplifier having a first input terminal, a second input terminal, and an output terminal, of which the first input terminal is connected to the signal input terminal and of which the second input terminal is connected through a third resistor to the output terminal of the operational amplifier itself and connected also to the output terminal of the amplifier; an analog-to-digital converter for performing analog-to-digital conversion on the output voltage of the operational amplifier; and a signal output terminal for outputting the digital signal produced by the analog-to-digital converter.


REFERENCES:
patent: 4562471 (1985-12-01), Eouzan et al.
patent: 4590458 (1986-05-01), Evans et al.
patent: 4972189 (1990-11-01), Polito et al.
patent: 5053770 (1991-10-01), Mayer et al.
patent: 5084700 (1992-01-01), Christopher
patent: 5105276 (1992-04-01), Schrock
patent: 6215427 (2001-04-01), Bonhoure et al.
patent: 0911976 (1999-04-01), None

Affiliated with

Also associated with

Rating

Analog-to-digital conversion device does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Analog-to-digital conversion device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Analog-to-digital conversion device will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2576960