WO1986001056A1

WO1986001056A1 - A sensor or transducer

Info

Publication number: WO1986001056A1
Application number: PCT/NL1985/000031
Authority: WO
Inventors: Wei-Jian Lian
Original assignee: Stichting Centrum Voor Micro-Elektronica
Priority date: 1984-07-20
Filing date: 1985-07-18
Publication date: 1986-02-13
Also published as: NL8402314A; EP0187808A1

Abstract

A sensor or transducer which is adapted to transform a measurable parameter into a digital signal representing the magnitude of said parameter, comprising a bistable unit with an element which is sensitive for said parameter, means for bringing said unit into the metastable state, means for counting the number of transitions towards one side or the other, and means for indicating the counting results, said number of transitions being influenced by said sensitive element in function of the magnitude of said parameter. Said bistable unit is, in particular, a symmetrical electrical bistable circuit having in one branch thereof an element which is sensitive for said parameter, the metastable state of said circuit being effected by interrupting the supply or applying an auxiliary voltage or current at a desired, and in particular high, frequency. Such a bistable element is, in particular, connected to a differential counter indicating the number of transitions towards one side and the other resp.

Description

A sensor or transducer.

There exist sensors or transducers for many parameters, by means of which the parameter to be measured can be transformed into a different parameter, generally an electrical current or vol¬ tage, the latter parameter being suitable for being transferred or processed for display or calculation.

A draw-back of such sensors is that the transformation takes place in an analogue way, whereas for processing a digital form is preferred, and that the sensitivity is often insufficient.

It is an object of the invention to remove these draw-backs, and to provide a sensor which is characterised by a bistable stage having an element which is sensitive for the parameter to be measu¬ red, by means for bringing said bistable stage periodically into a metastable condition, by means connected to at least one output of said stage for counting, during a predetermined period, the number of transitions from the metastable condition towards one side or the other, and by means for indicating the counting result.

In the metastable condition, if the circuit is perfectly symmetrical, the transition is determined by the always present noise, so that, since noise is a random phenomenon, the number of transitions towards one side within a sufficiently long measuring period will be equal to that towards the other side. As soon as an asymmetry arises, for instance because the sensitive element of this circuit experiences a change by an external influence, the distri¬ bution of the number of transitions will deviate from the 0,5: 0,5 ratio, until at a given intensity of the external influence the

1,0: 0 ratio is reached so that, then, the sensor is saturated. This process is dependent on the intensity of the external influence. As soon as the relationship has been determined by calibration, the value of the parameter to be measured can be derived from the count of the transitions. As the number of transitions is larger, the accuracy of the measurement will be better accordingly.

Although bistable circuits with one single branch are known, generally bistable circuits with two branches are preferred which ar connected to a common supply, since such circuits can be made perfectly symmetrical.

In practice mostly an electrical bistable circuit will be used which is preferably realised as an integrated circuit, since, then, both branches can be made accurately symmetrical. If a high switching frequency is used, such measurement statistics will be obtained within a short period that an accurate measurement is possible. Frequencies of the order of magnitude of 0, 1 MHz have appeared to be possible, which provides a sufficient basis for de¬ pendable statistics. This frequency is limited by the switching time of the bistable stage. Furthermore, by supplying an auxiliary current, it is possible to influence the sense of an equilibrium disturbance, either for adjusting the equilibrium, for removing a shift, or for bringing about an equilibrium shift serving as a presetting, so as to obtain the desired measuring conditions. A metastable condition can be brought about in various ways, such as by briefly interrupting the supply of the bistable stage, or by applying signals with a given intensity and duration to the or each set input.

For the utilised transition phenomenon from the metastable condition an accidental disturbance is required which is provided by the always present noise. If said noise is insufficient, also an artificial noise can be supplied, for instance in the form of a sine or saw-tooth current, and the frequency thereof should, as a matter of fact, be chosen in respect of the transition frequency so that a statistically dependable result is obtained. A plurality of sensors of this kind can be combined into an assembly which is adapted to determine the parameter to be measu¬ red in different points, the inputs and outputs of the bistable stages then being connected in the form of a register, means being provided for reading out the numbers represented by the counting positions of these stages on suitable instants.

Such an assembly can, in particular, be used for deter¬ mining the distribution of a parameter, each stage then being driven to saturation or not, and then a binary representation of the distri¬ bution is obtained. In particular the bistable stages can be inter¬ connected in the form of a shift register.

The invention will be elucidated below in more detail by reference to a drawing, showing in: Fig. 1 a diagrammatical representation of a bistable electrical circuit; and

Fig. 2 a block diagram of a complete sensor circuit of the invention.

In Fig. 1 an electrical bistable circuit is^' shown in a generalised form. This circuit comprises two switching elements la and lb, in particular, as shown, transistors, the position of the emittors and collectors not being indicated since this will depend on the type of the transistors, and, as the case may be, also field- effect transistors can be used. Said transistors are each connected between two supply terminals 2a, 3a and 2b, 3b resp., said terminal pairs being con¬ nected to a suitably polarised current source, and, of course the terminals 2 and 3 resp. of both branches can be mutually coupled. Resistors 4a, 5a and 4b, 5b resp. are provided between said termi- nals and the transistors 1a or lb resp., said resistors providing a suitable voltage at the transistors, and, for the rest, any one of said resistors, with the exception of the resistors 4a and 4b, can be omitted if desired.

Additional resistors όa and 6b are connected to the base of the corresponding transistor lb and la resp., and are included in a respective cross-connection connected to one of the electrodes of the other transistor. If required resistors 7a and 7b are provi¬ ded for adjusting the base voltage, said resistors, on the other hand, being connected to terminals 8a and 8b resp. which, for in¬ stance, can be interconnected or can be connected to the terminals 3a and 3b resp., depending on the prevailing voltage distributions. Additional terminals 9a and 9b can serve for determining the condition of the bistable circuit, and, as the case may be, for supplying a transition signal.

The operation of such a circuit is known, and a detailed description thereof is, therefore, not necessary. In the stable condition one of the transistors 1 is conducting, and the voltage drop over the associated resistor 4 will, then, maintain the base junction of the other transistor 1 unambiguously in the non-con¬ ducting region, and, when the condition is reversed, the change of these voltages supports the transition.

If, however, the circuit is in a metastable condition, e.g. immediately after supplying the supply voltage or when, by applying suitable voltages at the terminals 9, both transistors are made conducting or non-conducting and these voltages are subsequent¬ ly removed, the circuit will switch over towards one of the stable conditions immediately thereafter. This can be a consequence of an asymmetry of the circuit, but in a perfectly symmetrical circuit noise phenomena will bring about said transition. In the latter case there is no preference for either condition so that, at a large number of transitions, 50 % of the transitions will take place to one and 50 % to the other side. In the former case it will depend on the degree of asymmetry and the intensity of the noise how many transitions will take place towards the one or the other side. Beyond a given asymmetry the noise does no longer play a role, and the transition will always take place towards one side.

According to the invention use is made of these phenomena. One starts, for instance, from a perfectly symmetrical semiconductor circuit, in particular an integrated circuit. The supply voltage is switched on and off a great number of times, and the number of tran¬ sitions is counted. Fig. 2 shows an example of a fundamental circuit arrangement, in which the terminals 9a and 9b of a bistable circuit 10 are connected to counting inputs 11a and lib resp. of a diffe¬ rential counter 12. The reached counting position can be read out at 13. A supply input 2 of the circuit 10 is connected to an a.c. source 14, e.g. a hf source adapted to switch the supply on and off a great number of times, e.g. at a frequency of the order of magni¬ tude of 0, 1 MHz, so that, in a short time, a sufficiently large number of transitions can be reached for obtaining dependable sta¬ tistics. If no 0,5: 0,5 distribution is obtained, this equilibrium condition can be set by adjusting one side, e.g. by means of an auxiliary current source, the total count then being zero.

If, now, one of the elements 1,4, 5, 6 and 7 is sensitive for a phenomenon to be measured, e.g. heat, radiation, electrical or magnetical fields etc., or one or more elements are included in the circuit which will produce a current or voltage responsive to such a phenomenon, the symmetry will be disturbed on the occurrence of such a phenomenon. This leads to a differential count at the out¬ put 13 which is a measure for the intensity of this phenomenon. The relationship between this intensity and the counting result is not necessarily a linear one, but can be determined by calibration.

The advantage of this procedure is that very small inten¬ sities can be measured with a high accuracy. The measurement range is, then, limited by that intensity which leads to 100 % transitions in one sense (saturation). Instead of determining the differential count it is also possible to supply an auxiliary current to one half of the bistable circuit which compensates the equilibrium disturbance and leads to a zero differential count. The intensity of this current is, then, a measure for the intensity of the measured phenomenon, counting being most sensitive around the zero point.

It is also possible to introduce, instead of the natural noise, an artificial noise with a suitable frequency and intensity into the circuit, by means of which the measurement range can be increased, this of course at the expense of the sensitivity.

It is also possible to use such a circuit as a memory element which is saturated by the phenomenon if the circuit is in the other condition, so that, from the fact that a transition occurs or not, the reached position can be derived.

In particular a plurality of such circuits can be juxta¬ posed in different points so that, then, the changes in the diffe¬ rent points can be represented in digital form, and are read out as such when resetting the respective circuits. Such an assembly can also be realised in matrix shape, and can, for instance, be used as a picture memory.

In the case of a bistable stage to be brought into the saturated condition the symmetry is no longer important, and then also other types of bistable circuits than the circuits of the symmetrical kind shown in Fig. 1 can be used.

Claims

C l a i s

1. A sensor or tranducer for a parameter to be measured, characterised by a bistable stage having an element which is sensitive for the parameter to be measured, by means for bringing said bistable stage periodically into a metastable condition, by means connected to at least one output of said stage for counting, during a predetermined period, the number of transitions from the metastable condition towards one side or the other, and by means for indicating the counting result.

2. The sensor of claim 1, characterised in that the bistable stage is a symmetrical bistable stage with two branches connected to a common supply.

3. The sensor of claim 1 or 2, characterised in that the bistable stage is an electrical bistable circuit which, in particular, is realised as an integrated circuit.

4. The sensor of claim 3, characterised in that it is adapted to work at a high switching frequency, in particular of the order of magnitude of 0, 1 MHz.

5. The sensor of claim 3 or 4, characterised by means for supplying an auxiliary current or voltage in the sense of an equilibrium disturbance.

6. The sensor of any one of claims 1..5, charac terised in that the metastable condition is brought about by briefly inter¬ rupting the supply of the bistable stage.

7. The sensor of any one of claims 1..5, charac terised in that the metastable condition is brought about by applying sig¬ nals with a given intensity and duration to the or each set input.

8. The sensor of any one of claims 1..7, characterised by means for supplying an artificial noise.

9. Assembly of sensors of any one of claims 1..8, adapted for determining the parameter to be measured in different points.

10. The assembly of claim 9, characterised in that the inputs and outputs of the bistable stages are connected in the form of a register, means being provided for reading out the numbers represented by the counting positions of the stages on suitable instances.

11. The assembly of claim 9 or 10, characterised in that the different bistable stages are adapted for being driven in¬ to the saturated condition.