DE102007048727A1 - Sensor device for use in e.g. integrated complementary metal oxide semiconductor-micro-electro-mechanical system circuit, has conversion device designed in such manner that digital signal is produced based on output signal - Google Patents

Abstract

The device has a chemically sensitive delay element (VZE) for influencing an input signal (V2) as a reaction of effects of a chemical medium with respect to temporal characteristics, where the input signal is converted into an output signal (out). A conversion device is designed in such a manner that a digital signal is produced based on the output signal. Another delay element is provided for influencing a clocked input signal based on the temporal characteristics, where the clocked input signal is converted into another output signal.

Description

The The invention relates to a sensor device.

In process measurement, analytics and chemosensitive applications It is increasingly of interest to convert chemical information into a microcontroller-compatible one Signal implement. Examples are the detection of toxic or explosive gases and the measurement and analysis of gas and ion concentrations. Today's chemical sensors rely on interaction with one chemical substance mass, temperature, light intensity, Resistance, capacity or potential changes into an electrical signal, its time, frequency, current or voltage is a measure of the gas or ion concentration.

was standing The technology is to time and frequency with a time-to-digital Converter (TDC) and the analog signals current and voltage with an analog-to-digital converter (ADC) microcontroller compatible prepare. By combining the CMOS technology with the MEMS (Microelectromechanical Systems) technology has been able to monolithically integrated chemical Manufacture sensors based on ADC. The TDC procedure, on the other hand has so far been predominantly associated with discrete resistive and capacitive sensors used, the electrical signals z. B. can be implemented by means of an RC element in periods.

The function of a TDC-based temperature sensor is, for example, in Chen et al., IEEE Journal of Solid State Circuits Vol. 8, Aug. 2005, pp. 1642-1648 " described. The application of a TDC in combination with a discrete chemosensitive sensor is described in "Brunsman, Tille, IEE Electronics Letters, Vol. 2, Sept. 2006 " described.

shortcomings known sensor devices based on the susceptibility their analog sensor signals and on the complexity of the used ADC circuits, as well as on the elaborate Switching logic for the use of TDC circuits and that stray capacitances and switching resistors the achievable signal resolution limit.

Of the Invention is now the object of the known sensor devices to improve.

These The object is achieved by the features of the independent claim solved. Advantageous developments of the invention are to refer to the dependent claims.

A Sensor device according to the invention has a Signal input for a clocked input signal on or it generates this itself. Also the feedback line is in the context of the invention, in particular in a TDC, as a signal input for a clocked input signal. By at least one first chemically sensitive delay element the input signal is in response to the action of a chemical medium (Gas, liquid, etc.) and optionally as a reaction to other environmental influences, such as temperature, in terms of temporal characteristics, for example in terms of the cycle time, the transit time or the phase shift, especially delayed, and in a correspondingly influenced implemented first output signal. A conversion device, such as a time-to-digital converter (TDC) is such set up that as a function of the first output signal a digital signal is generated.

Thereby is achieved by the sensor device directly one of the Influence of a chemical medium, for example on the concentration of a chemical medium, generates dependent digital signal becomes.

By a preferably adjustable cycle time of the input signal can the ratio of cycle time to delay time be set. For at a periodic beat, which is to increase the signal-to-noise ratio, for example, by averaging, is advantageous, the cycle time should be greater than that Be delay time.

According to one preferred embodiment of the invention is a second particular similar delay element provided by which the or a clocked input signal, in particular in response to Operating voltage and environmental influences, such as the temperature, in terms of temporal characteristics and influences is converted into a second output signal. The second delay element is used as a reference delay element in terms of chemical medium, for example in terms of concentration of the chemical medium used and is therefore less chemically sensitive as the first retarder or chemically essentially not sensitive at all. The conversion device is now set up so that, depending on the first output signal and the second output signal a digital Signal is generated.

Prefers is provided that the delay time of at least one the two delay elements electrically adjustable is. This allows the connection to a reference clock by means of a delay locked loop. The setting is done, for example in CMOS inverters by the bias current.

For example both delay elements are based on a CMOS inverter, a CMOS transmission gate or a CMOS pass gate.

Preferably the conversion device is set up such that depending on the influencing difference, for example the running time difference or the phase shift, or the influencing ratio, for example, the term ratio, between the first Output signal and second output signal generates a digital signal becomes.

The Delay element preferably comprises a chemosensitive Field effect transistor and / or a resisitven sensor and / or a capacitive sensor.

Under Influence of the chemical substance is when using a chemosensitive Field effect transistor a threshold, in particular the threshold voltage VTO, the field effect transistor shifted, when using a resisitven Sensors changed the sensor resistance or during use a capacitive sensor changes the sensor capacity

Preferably are used to increase the resolution and thus to Improvement of the measuring accuracy at least two delay elements, each comprising the first and second delay elements, connected in series.

advantageously, At least one delay element is part of one cyclic time-to-digital conversion structure (TDC). this has the advantage that the TDC itself is sensitive and not just the measuring element. In addition, cyclic TDCs provide a very compact TDC structure.

alternative this is, for example, at least one delay element Part of a vernier delay line (VDL) or another structure, on which is based on a time-to-digital conversion.

Preferably is the sensor device in an integrated CMOS or CMOS MEMS circuit realized. Through a monolithically integrated realization in CMOS MEMS technology has a high potential in a small footprint and low power versus versions with more discrete Sensor technology created. In this case, advantageously, the circuit layout the two delay elements in each delay element designed so that cross sensitivities, especially against Fluctuations in operating voltage and temperature, as well against other chemical substances, such as. As moisture, minimized become.

Especially preferred is the use of a periodic input signal with an output downstream digital low-pass filter to for example, by averaging the signal-to-noise ratio to improve.

By another delay element or another delay line with fixed delay can the sensitivity the sensor device are calibrated by, for example, the chemically generated transit time difference with the fixed "calibration difference" is compared. Through a DLL method can be fluctuations the operating voltage can be compensated by, for example, a Connection to a reference clock by means of a delay locked loop he follows.

The proposed innovations thus relate in particular to the realization a fully digital chemical sensor whose chemically sensitive elements preferably integral components of a time-to-digital converter are, making it a conversion of an analog electrical signal no longer needed in a digital signal.

• – Reduzierung der Kosten für chemische Sensoren durch Vollintegration in Halbleitertechnologie;
• – Verringerung der Sensorsystemgeometrie durch integrierte Ansteuer-/Auswerteelektronik in Halbleitertechnologie (Single-Chip-Lösung);
• – Reduzierung des Systemherstellaufwandes gegenüber diskreten Bauelementen und damit eine Erhöhung der Prozesssicherheit und des Qualitätsniveaus;
• – Reduzierung von parasitären Kapazitäten und Widerständen gegenüber diskreter Aufbau- und Verbindungstechnik;
• – Reduzierung der Störanfälligkeit bei der Übertragung eines analogen Ausgangssignals zur Wandlerstufe, damit eine Erhöhung des Signal-Rausch-Verhältnisses und damit eine Erhöhung der Messgenauigkeit;
• – Reduzierung der Leistungsaufnahme durch die Sensoreinrichtung.

In particular, one or more of the following advantages are achieved by the invention or its developments:

• - Reduction of the cost of chemical sensors through full integration in semiconductor technology;
• - Reduction of the sensor system geometry by integrated control / evaluation electronics in semiconductor technology (single-chip solution);
• - Reduction of the system production effort compared to discrete components and thus an increase in process reliability and quality levels;
• - Reduction of parasitic capacitances and resistances compared to discrete assembly and connection technology;
• - Reduction of the susceptibility to interference when transmitting an analog output signal to the converter stage, thus increasing the signal-to-noise ratio and thus increasing the accuracy of measurement;
• - Reduction of power consumption by the sensor device.

in the The invention will now be described by way of example with reference to FIG to the following figures:

1 shows a simplified circuit diagram of an inverter as a delay element;

2 shows a simplified circuit diagram of an inverter as a delay element;

3 shows a simplified circuit diagram of a clocked delay element;

4 shows a simplified block diagram of a delay element;

5 shows a simplified block diagram of a digital chemical sensor with ring oscillators and downstream TDC or frequency counter;

6 shows a simplified block diagram of a digital chemical sensor with cyclic TDC structure;

7 shows a simplified block diagram of a digital chemical sensor with VDL TDC structure.

This in 1 shown delay element VZE is designed as an inverter, in particular as a CMOS inverter, and includes one or two MOSFETs Q1, Q2, which are chemically sensitive.

Become in a CMOS inverter, one or two chemically sensitive MOSFETs or ion-selective ISFETs so shifts under Exposure of a chemical substance to the threshold VTO of the corresponding Transistor. In a simple model of the inverter is calculated then the propagation delay TP of the clock pulse V2 (input signal) at the

Output out of the inverter to: TP = (C L · L / W) / (.mu.C ox (V1 - VTO)) · In ((1.5 · V1 - 2 · VTO) /0.5 · V1).

Therein L and W denote the gate length and width of the transistors, C _L the load capacitance, C _ox the gate capacitance and μ the charge carrier mobility. If the operating voltage V1 is not chosen to be large compared to VTO, TP changes measurably with VTO.

This in 2 Delay element VZE shown differs from that shown in FIG 1 shown delay element in that, alternatively or in addition to the at least one MOSFET, a resistance sensor R2 and / or a capacitive sensor C3 are chemically sensitive. The propagation delay can then alternatively or additionally be achieved by an action of a chemical substance on the resistance sensor R2 or the capacitive sensor C3, as shown here by way of example for the n-channel FET Q1.

3 shows a clocked delay element VZG, which contains two delay elements VZE1, VZE2. Since the propagation delay of the chemically sensitive delay element VZE1 also depends on the operating voltage V1 and the operating temperature, a second, chemically less or chemically less sensitive but otherwise physically similar delay element VZE2 is used in the delay element VZG. The circuit layout is designed so that process and manufacturing tolerances essentially do not affect. If both delay elements VZE1, VZE2 in the delay element VZG are fed by the same operating voltage V1 and the same clock pulse V2 (input signal), the time difference between the output signals out1, out2 is a measure of the chemically effective quantity, in particular the concentration of the chemical substance.

4 2 shows a simplified representation of a delay element VZG with an input "in" for the clocked input signal, a delayed output signal "out c" of the chemically sensitive delay element VZE1 and a delayed output signal "out" of the chemically insensitive delay element VZE2 Delay effect can be increased and / or there are different sensor structures (see 5 . 6 and 7 ).

5 shows a digital chemical sensor device with ring oscillators and downstream time-to-digital converter TDC or frequency counter. In the 5 Delay elements shown in the upper row (the output of each of which is denoted by out c) of the delay elements are connected by a series connection and by means of a feedback line to a ring oscillator, as well as the delay elements shown in the lower row.

Other than in the example according to 4 the two delay lines have no common input. The oscillation time / frequency of the upper oscillator, which is evaluated with a TDC / frequency counter, is chemically sensitive, that of the lower oscillator, which is also evaluated with a TDC / frequency counter, is not. The chemical information then results from the resulting difference or the ratio of the TDC / frequency counter signals.

6 shows an exemplary embodiment of a digital chemical sensor device with cyclic TDC structure. Analogous to 5 The upper and lower delay elements (each paired together to form a delay element VZ1, VZ2, VZn) are each interconnected to form a cyclic TDC.

In the cyclic TDC structure has at least one delay element of each delay line or at least one coupling element (here exemplified AND and OR gates with the inputs gen: "in", "Reset") a channel width which is larger by a factor β, than that of all other gates. This results in a discrete shortening of the pulse width each time the pulse fed in "in" passes, until the output pulse can finally no longer be detected.

A counter Z counts the number of detectable output pulses to an input pulse input. In a simple model, the reduction in pulse width per cycle is proportional to the following factor: ΔW ~ (β-1 / β) * 2 * VTO / (V1-VTO) 2 + 1 / (V1 - VTO) · In ((1.5 · V1 - 2 · VTO) /0.5 · V1).

design parameters are the transistor layout (especially the factor β), the number of delay elements in each delay line and the width of the injected clock pulse. They become so on each other tuned that the input pulse is shorter than the shortest of the duration of the pulse through the delay lines and that a sufficient measurement resolution is achieved. A comparison of the counts of the chemically sensitive and of the non-sensitive branch provides the chemical information. The reset pulse is required to start the cyclic TDCs the measurement in the stable initial state ("out", "out c ".)" Low "and, if necessary, the counters reset.

7 shows a digital chemical sensor device with VDL (Vernier Delay Line) -TDC structure in which the delay elements VZE are embedded. The low-high transitions of the start and stop pulses are fed into the delay lines with a defined time interval. The propagation delay is greater in this example in the chemically sensitive delay line than in the comparison line, the clock edge of the start pulse lies before the clock edge of the stop pulse. During the pulse passes through both delay lines, each D flip-flop compares which pulse comes first. The digitally coded position in the delay line, where the stop signal has caught up with the start signal, provides the chemical information with a resolution corresponding to the propagation time difference of the delay elements.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited non-patent literature

• - "Chen et al., IEEE Journal of Solid State Circuits Vol. 8, Aug. 2005, pp. 1642-1648 " [0004]
• - "Brunsmann, Tille, IEE Electronics Letters, Vol. 2, Sept. 2006 " [0004]

Claims (9)

sensor device - with a signal input (in) for a clocked input signal, - With at least one first chemically sensitive delay element (VZE1), through which the input signal in response to the action a chemical medium in terms of temporal characteristics is influenced and converted into a first output signal (out1), and - With a conversion device (TDC), the is set up such that, depending on the first Output signal (out1), a digital signal is generated. Sensor device according to claim 1 - With a second delay element (VZE2), through which the clocked input signal with respect to the temporal characteristic and converted into a second output signal (out2), wherein the second delay element as a reference delay element less chemically sensitive than the first retarder (VZE1) - at which the conversion device (TDC) is set up such that in dependence on the first output signal and the second output signal is generated a digital signal. Sensor device according to one of the preceding claims, in which the conversion device (TDC) is set up in this way is that, depending on the influencing difference between the first output signal and the second output signal a digital one Signal is generated. Sensor device according to one of the preceding claims, in which the delay element (VZE, VZE1) is chemosensitive Field effect transistor includes. Sensor device according to one of the preceding claims, in which the first and the second delay element (VZE1, VZE2) form a delay element (VZG), and at least two Delay elements (VZG1, VZG2) connected in series become. Sensor device according to one of the preceding claims, at least one delay element (VZG1) component a cyclic time-to-digital conversion structure (TDC). Sensor device according to one of the preceding claims, at least one delay element is part of a Vernier delay line, on whose structure a time-to-digital conversion is based. Sensor device according to one of the preceding claims, which realized in an integrated CMOS or CMOS MEMS circuit is. Sensor device according to one of the preceding claims, in which a periodic input signal is used, the one digital filtering of the output signal allows.