ES2310439A1 - Low consumption circuit for a capacitive transducer (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Low consumption circuit for capacitive transducer, formed by two chains (1 and 4) of logic gates (2), in which capacitors (3) and capacitors (5) are respectively interleaved, of which at least some, for example capacitors (3), are of variable capacity, and the others, for example the capacitors (5), are of fixed capacity or of a variable capacity of opposite sign to the capacitors (3), depending on the physical quantity to be measured, so that with an excitation applied to both chains (1 and 4), these produce signals with different delays, whose difference is a function of the measured physical quantity. (Machine-translation by Google Translate, not legally binding)

Description

Low consumption circuit for a transducer capacitive

Technical sector

The present invention is related to capacitive transducers that are used to measure quantities of any type, proposing an electronic circuit for said transducers, with which it is possible to reduce significantly power consumption, thereby improving the chances of Useful application thereof.

State of the art

Capacitive measurement transducers are based  in the variation of the capacity of one or several capacitors sensitive to the magnitude to be measured, so that measuring said variation you can know the value of the magnitude that is measured, using an electronic circuit that transforms the variation of the capacity in a variation of voltage or of electric current.

Various solutions to measure are known magnitudes in that sense, so that, for example:

US Patent 4065715 describes a type of transducer based on a circuit capable of generating a pulse type signal, the duration of which is proportional to the value of the magnitude to be measured, the circuit comprising a capacitor in parallel with an electrical resistor, of which one is variable with the magnitude to be measured, so that the duration of the capacitor's charge or discharge pulse depends on the time constant of the resistance-capacitor circuit. This solution results from a high consumption in operation, due to the use of a resistor
electric

US Patent 4342230 describes a sensor of pressure that transforms the pressure into a pulse whose duration is function of said pressure. In this case it is about measuring a pressure by a mechanical means and not by an electronic circuit and therefore it is not a capacitive sensor.

US Patent 6288587 describes an element that transforms a pulse of time into a digital signal, which is not a circuit that transforms a physical magnitude into a pulse of time whose duration is a function of said physical magnitude.

EP 1363404 describes the obtaining of an output signal from a sensor, using an encoding based on pulse width, which is treated in a particular way of coding, based on the ratio of the duration of the states Logical low and high.

Now, in most applications  Capacitive transducers work with digital signals, for which a Digital Analog Converter (ADC) is used, through which the signals corresponding to the voltage or current variations that are obtained with the transducer, said ADC assuming additional consumption.

On the other hand, in the applications in which The transducers are powered by a battery, it is it is necessary to minimize consumption to extend the duration of the power, which is even more needed in applications in which the transducers are fed by means such as radiofrequency, light, heat, vibrations, etc.

Therefore, the ideal is to have transducers of very low consumption, in which the need to eliminate transform the measured magnitude into an electrical signal and subsequently do a conversion analog-digital signal obtained.

Object of the invention

In accordance with the present invention it is proposed a circuit that allows to achieve the mentioned objective, by a simple embodiment that provides very functional features advantageous

This circuit object of the invention consists of a chain of logic gates with fixed capacity capacitors interspersed and another chain of logical gates in which it capacitors interspersed whose capacity varies with the magnitude Physics to measure.

A set is thus obtained, in which applying excitation to the input of both chains, provides at the exit of the chains, two signals with different delays, one of which serves as a reference, while the other is function of the measured physical magnitude, so that the difference of  delays allow to determine the value of the physical magnitude to to size.

The outputs of the circuit chains are they can combine through a logic gate, which allows to obtain a pulse whose duration is a function of the physical magnitude that is measured and therefore for the duration of said pulse can be determined the value of the physical quantity under measurement.

It is therefore a circuit that Transforms capacitor capacity variations used as sensitive elements, in a difference of signal delays, which can be transformed into a pulse whose duration is function of the physical quantity to be measured.

This circuit allows replacing the use of a Digital Analog Converter by electronic circuits much simpler, to digitize the resulting signal, since the time (difference in signal delays or pulse duration) can be digitized immediately, for example by employment of accountants.

This results in a very low circuit. consumption, since its components (capacitors and transistors working in switching) are elements of low consumption, while that a time to signal converter can be used at the output digital, which is simpler to implement and has lower consumption that the Digital Analog Converters used in the conventional solutions

Therefore, said circuit object of the invention results from certainly advantageous features, that give it its own life and preferential character of application for the capacitive transducers found destined.

Description of the figures

Figure 1 shows a circuit diagram recommended according to the invention, where the number of logic gates and capacitors may be higher or lower as desired or increased decrease the difference in delays between the two chains.

Figure 2 is a graphic example of the duration of an output pulse depending on the variation of the variable capacities in the recommended circuit.

Detailed description of the invention

The object of the invention relates to a circuit intended for a capacitive measurement transducer, with an embodiment that allows to obtain at the output a signal by the that you can determine the value of a physical quantity that is subjected to measurement, with a very low power operation.

The circuit that is recommended comprises a chain (1) of logic gates (2), in which they are inserted capacitors (3) of varying capacity depending on the magnitude physics to be measured, and another chain (4), also with logic gates (2), in which capacitors (5) of fixed capacity and independent of the physical quantity to be measured.

A circuit is thus obtained in which subjecting to both chains (1 and 4) to an excitation, are obtained in the respective outputs two signals with different delays, so that the difference in said delays is a function of the magnitude Physical subject to measurement, allowing to determine the value of is.

The same effect can be achieved by two chains (1 and 4) integrated with respective capacitors (3 and 5) variables, the capacitors (3) and the capacitors (5) being both chains (1 and 4), sensitive to the physical quantity to be measured, with sensitivities of opposite signs.

The determination of the value of the physical magnitude  measurement can be established by comparison between the signals of output of the two chains (1 and 4), by means of the difference of delays of said signals, but such output signals can be also pick up at a logic gate (6), which combines the signals to produce a pulse whose duration is a function of the measured physical magnitude, thus allowing to determine the value of said physical magnitude.

The circuit therefore transforms the capacitor capacity variations (3) that are employed as sensitive elements, in a difference of delays between chain (1) with variable capacitors (3) and chain (4) with capacitors (5) of fixed capacity that are used as reference, to create a pulse whose duration is a function of the physical magnitude measured, according to the graph in figure 2 represented by way of example, which represents the duration of the pulse in nanoseconds depending on the capacity variation of the capacitors (3) in femtofaradios.

If you want to digitize the output signal, the circuit allows to use electronic circuits for this purpose more simple than a digital analog converter, since the difference Signal delay or pulse duration is a function of time that can be digitized immediately, by example the use of counters, resulting in the whole set Very low consumption function, since both the components of the own circuit, like the output circuits attachable to it, propitiate that characteristic of low consumption.

Claims (5)

1. Low consumption circuit for a capacitive transducer, of the type intended to measure physical quantities by means of a signal depending on the value of the physical quantity that is subjected to measurement, characterized in that it consists of a chain (1) of logic gates (2), in which capacitors (3) are interleaved whose capacity varies depending on the physical quantity to be measured, and another chain (4), also with logic gates (2), in which capacitors (5) are interleaved whose capacity remains constant with independence of the physical quantity to be measured, so that with an excitation applied to both chains (1 and 4) they produce output signals with different delays, the difference of which is a function of the measured physical quantity. 2. Low consumption circuit for a capacitive transducer, according to the first claim, characterized in that the value of the measured physical quantity is determined by direct comparison of the output signals of the chains (1 and 4), and is a function of the difference in delays of the corresponding signals. 3. Low consumption circuit for a capacitive transducer, according to the first claim, characterized in that the value of the measured physical quantity is determined by the duration of a pulse generated by a logic gate (6), in which the output signals of the chains (1 and 4). 4. Low consumption circuit for a capacitive transducer, according to the first to third claims, characterized in that the signal resulting from the difference in delays of the signals of the chains (1 and 4) or corresponding to the duration of a generated pulse depending on the difference in delays, it is immediately digitized by means of low consumption devices, such as counters. 5. Low consumption circuit for a capacitive transducer, according to the first to fourth claims, characterized by comprising two chains (1 and 4) integrated, respectively, with capacitors (3) and capacitors (5) that are sensitive to magnitude physics to be measured, with sensitivities of opposite signs.