Coded data generation or conversion – Analog to or from digital conversion – Analog to digital conversion
Reexamination Certificate
2002-07-16
2004-02-17
Jeanglaude, Jean (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Analog to digital conversion
C320S132000, C324S428000
Reexamination Certificate
active
06693577
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an integration type A/D conversion method, an integration type A/D converter, and a battery charger utilizing the integration type A/D converter, suitable for measurement of integrated DC currents.
BACKGROUND OF THE INVENTION
Batteries are used in a variety of fields including notebook type personal computers (PC), personal digital assistants (PDAs), digital still cameras (DSC), smart-phones, electric automobiles, and motor-assisted bicycles.
Batteries such as lithium ion batteries for use in notebook PCs are likely to burst if they are overcharged during charging. On the other hand, if they are discharged exceedingly above its allowable limit, their charging/discharging characteristics are deteriorated.
In order to circumvent such incidents, and take advantages of the battery performance, appropriate charging and discharging control suitable for the charging/discharging characteristics is required. For this purpose, there have been implemented in the past measurement devices for monitoring charging and discharging status of batteries.
A typical discrete measurement device measures a charging/discharging current that varies over a wide range (e.g. 0.5 mA−15 A), converts it to a voltage (5 &mgr;V−150 mV) and holds sampled voltage after it is amplified. This type of measurement device also includes a micro-controller unit (MCU) for converting the voltage into a digital signal by means of a multi-bit (e.g. 10 bits) sequential comparison type A/D converter and for averaging the data obtained.
Since the conventional measurement device integrates the charging/discharging current by accumulating the product of sampled discrete value and the sampling period, the integrated value inevitably has an error. In addition, precise measurement is difficult due to the fact that, since the dynamic range of the input signal is large, the measurement is influenced by a persistent weak current and noise. Further, in order to obtain practical accuracy in the averaging process, it is necessary to repeat a prolonged measurement using an MCU that consumes a fairly large current, which makes it difficult to reduce energy consumption.
FIG. 1
is a block diagram showing a conventional integration type A/D converter for integrating a continuous variable and converting it into a digital variable through A/D conversion.
FIG. 2
is a timing diagram of the converter.
As seen in
FIGS. 1 and 2
, the integration circuit
701
of the converter is initially reset, providing zero Volt as the output Ea thereof (the output of the integration circuit hereinafter referred to as integral output voltage). Under this condition, a start pulse s is applied to a flip-flop
703
, which turns on switch S
1
and turns off switch S
2
to couple the converter to an input signal Ei. Then the integration circuit
701
starts integration of the input signal Ei, generating an output voltage−Ei/RC. If the output Ea exceeds a comparative voltage−&Dgr;Vt, a comparative pulse p is generated, starting a first period of integration (the period hereinafter referred to as integration period). The integration period Ts is the time basis of the measurement.
AND circuit
706
is now opened to cause counter
704
to count the number of clock pulses issued from clock generator
705
. As the count of the counter
704
reaches an overflow value Nm after a period Ts, an overflow pulse r is generated to reset the flip-flop
703
.
Next, the switch Si is turned off and switch S
2
turned on, switching the connection to a reference voltage of −Es, starting the integration of the current in a second integration period T. This results in an output of the integration circuit
701
having an opposite slope Es/RC as compared with the first integration. As the output Ea returns to −&Dgr; t, the output of comparator
702
is inverted, closing the AND circuit
706
. During this period, the counter
704
has been again counting the clocks starting from
1
after the overflow. The count N of the counter
704
at the time the AND circuit
706
is closed is proportional to the input signal Ei.
The value of the integration obtained by the integration circuit
701
in the first half of the integration is proportional to the level of the input signal Ei, while in the second half integration in the reverse direction the period T of integration is proportional to the level of the input signal Ei. That is, Ei·Nm=Es·N. Thus, the input signal Ei (=N·Es/Nm) is A/D converted by counting the clock pulses N during the period T. Such conventional integration type A/D converter has advantages in that it is not costly assembled and not strongly influenced by noise
However, conventional A/D converters are limited in dynamic range, so that when the input current has a wide range of variation, as in the case of charging or discharging a battery, it is difficult to perform precise measurements using these converters. Moreover, in order to complete the A/D conversion quickly, the clock must have a high frequency, which disadvantageously results in a problem of large power consumption.
SUMMARY OF THE INVENTION
Thus, the invention is directed to solve the above mentioned problems pertinent to conventional A/D conversion circuits by providing an improved integration type A/D converter.
In accordance with one aspect of the invention, there is provided an integration type A/D converter, which comprises:
an integration circuit for integrating an input signal to generate an integral output voltage (hereinafter referred to as integral output voltage);
an integral output voltage reduction circuit for bringing said integral output voltage back to the initial level thereof by a predetermined magnitude per unit time upon receipt of a signal instructing reduction of said integral output voltage (said signal hereinafter referred to as integral output voltage reduction signal);
a comparison circuit having at least one comparator for comparing said integral output voltage with a predetermined magnitude to generate a comparative output;
a counter for counting clocks upon receipt of a signal instructing counting clocks (said signal hereinafter referred to as count instruction signal); and
a control circuit for generating, upon receipt of said comparative output, said integral output voltage reduction signal and for generating said count instruction signal.
In accordance with another aspect of the invention, a battery charger is provided which is equipped with the A/D converter as described above.
In accordance with a further aspect of the invention, there is provided an integration type A/D conversion method, comprising:
a first step of integrating an input signal to generate an integral output voltage;
a second step of comparing said integral output voltage with a predetermined value to generate a comparative output;
a third step of generating an integral output voltage reduction signal and a count instruction signal upon receipt of said comparative signal;
a fourth step of bringing said integral output voltage back to the initial level thereof by a predetermined magnitude per unit time upon receipt of said integral output voltage reduction signal; and
a fifth step of counting clocks upon receipt of said count instruction signal to output the digital-value of the clocks counted.
REFERENCES:
patent: 4153867 (1979-05-01), Jungfer et al.
patent: 5769873 (1998-06-01), Zadeh
patent: 5841284 (1998-11-01), Takahashi
patent: 6081140 (2000-06-01), King
patent: 6157170 (2000-12-01), Noda et al.
Hogan & Hartson
Jeanglaude Jean
Rohm Co., LTD
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