CN201364365Y - Device for signal conditioning or capacitance detection of small-capacitance sensor - Google Patents

Abstract

The utility model provides a device for the signal conditioning or capacitance detection of a small-capacitance sensor. The device comprises a detection terminal, a receiving terminal and a screened cable, wherein the detection terminal is used for generating two groups of TTL pulse sequences which have the pulse widths respectively in direct proportion to the capacitance values of a capacitor to be tested and a reference capacitor by an oscillator circuit connected with the capacitor to be tested, and converting the two groups of TTL pulse sequences to low-voltage differential signals to facilitate long-distance transmission; the receiving terminal is used for receiving the low-voltage differential signals, restoring the differential signals to the TTL pulse sequences, further outputting analog voltage signals which have the amplitudes in direct proportion to the pulse widths of the pulse sequences, and quantifying the analog voltage signals to obtain the capacitance values of the capacitor; and the shielded cable is used for outputting the low-voltage differential signals from the detection terminal to the receiving terminal. The device with the above structure can achieve the signal conditioning or capacitance detection of the small-capacitance sensor in a limited space of the detection terminal or severe work conditions, and has the advantages of large dynamic detection range, low work voltage, simple structure, small size, easy integration, and long-distance reliable signal transmission.

Description

The device that is used for little capacitive transducer signal condition or capacitance detecting

Technical field

The utility model relates to a kind of signal condition or pick-up unit, particularly a kind of device that is used for little capacitive transducer signal condition under the abominable occasion of test side limited space or condition of work or capacitance detecting.

Background technology

At present, the common methods that is used for capacity measurement comprises bridge method, resonance method, frequency method etc., but when being to use these methods to be used for little capacitive transducer signal condition and little capacitance detecting, use the complex structure of the related device of these methods, be difficult to integratedly or microminiaturized, be difficult to use in test side limited space or the more abominable occasion of condition of work.

National Semiconductor (National Semiconductor) provides a kind of scheme (seeing " Typical Applications/Capacitance Meter " in the LM2907/LM2917 tables of data) that constitutes C meter with monolithic frequency-voltage converter LM2907/LM2917.Usually, voltage-frequency converter or frequency-voltage converter require to connect enough big electric capacity to keep steady operation (requiring to connect capacitance more than 500pF as LM2907/LM2917), if require output voltage and capacitance to keep the demand (usually require be better than 1%) of good linear relationship, then the electric capacity lower limit required higher (being generally several nanofarads) to satisfy capacitance detecting.Therefore, general being difficult to is directly used in little capacitive transducer signal condition of pico farad level or capacitance detecting with voltage-frequency converter spare.

The utility model content

The purpose of this utility model is to provide a kind of device that is used for little capacitive transducer signal condition or capacitance detecting, be convenient under the more abominable occasion of test side limited space or condition of work, little capacitive transducer be carried out signal condition or capacitance detecting, simple in structure, be easy to integrated.

The technical matters that the utility model solved can realize by the following technical solutions:

A kind of device that is used for little capacitive transducer signal condition or capacitance detecting is characterized in that it comprises:

By the oscillatory circuit that connects testing capacitor produce two groups of pulsewidths be proportional to respectively the appearance value of testing capacitor and reference capacitor the appearance value TTL pulse train and be converted to the test side that Low Voltage Differential Signal is beneficial to long-distance transmissions; Receive described Low Voltage Differential Signal and be reduced to the analog voltage signal that the also further output amplitude of TTL pulse train is proportional to the pulse train pulsewidth, can draw the receiving end of the appearance value of described capacitor after the quantification; And the shielded cable that described Low Voltage Differential Signal is transferred to described receiving end from described test side.

Described test side comprises:

A signal generating module that is used to produce clock signal;

A sensing module that produces TTL pulse train by described clock signal, testing capacitor and reference capacitor;

And the TTL pulse train that described sensing module is produced is converted to the sending module that Low Voltage Differential Signal is beneficial to long-distance transmissions.

Described receiving end comprises:

A receiver module that described Low Voltage Differential Signal is reduced to TTL pulse train;

And output module that described TTL pulse train is converted to analog voltage signal.

When the related device of the utility model is used to little capacitive transducer signal condition or detects the little electric capacity of pico farad magnitude, be the analog voltage signal that improves the output of described receiving end the linearity to described testing capacitor capability response, and reduce the influence of pulse rise and fall fringe time width and stray capacitance, offset capacitor device that capacity is bigger in parallel at described testing capacitor two ends, and the known appearance value of reference capacitor and offset capacitor device equate, thereby make the difference of amplitude of the analog voltage signal of corresponding output module output be proportional to the appearance value of institute's survey capacitor.

By changing the parameter value of signal generating module and sensing module in the described test side, can adjust described Device Testing dynamic range and the output gain that is used for little capacitive transducer signal condition or capacitance detecting; During adjustment, the cycle of the clock signal that described signal generating module produces should be less than the maximum pulse width of the TTL pulse that detects the pairing described sensing module output of dynamic range headroom.

The device that is used for little capacitive transducer signal condition or capacitance detecting that the utility model is related, adopt said structure, can under the more abominable occasion of test side limited space or condition of work, realize little capacitive transducer signal condition or capacitance detecting, dynamic detection range is big, operating voltage is low, and is simple in structure, and volume is little, especially be easy to integrated, can be on long distance the reliable transmission signal.

Description of drawings

Fig. 1 is the synoptic diagram of the related Device Testing end of the utility model;

Fig. 2 is the synoptic diagram of the receiving end of the related device of the utility model;

Fig. 3 is the signal sequence synoptic diagram of the related device of the utility model;

Fig. 4 is the synoptic diagram of test side when the related device of the utility model is used to the little electric capacity of little capacitive transducer signal condition or detection pico farad magnitude.

Embodiment

For realization technological means of the present utility model, feature and effect are understood easily,, further set forth the utility model below in conjunction with concrete diagram.

Embodiment 1

A kind of device that is used for little capacitive transducer signal condition or capacitance detecting as shown in Figure 1, 2, it comprises: test side 1 and receiving end 2, test side 1 is connecting testing capacitor C _S, and the inner known and stable reference capacitor C of appearance value that installed ₀ Test side 1 produces two groups of pulsewidths and is proportional to C respectively _SAnd C ₀The TTL pulse train of appearance value, and be converted to two groups of Low Voltage Differential Signals and transmit by shielded cable, the described Low Voltage Differential Signal that receiving end 2 will receive is reduced to TTL pulse train earlier, converts two groups of analog voltage signals then to, its amplitude is proportional to C respectively _SAnd C ₀The appearance value, can calculate described capacitor C after the quantification _SThe appearance value.

Referring to Fig. 1, test side 1 comprises: signal generating module 11, a sensing module 12 and a sending module 13; Signal generating module 11 produces a row clock signal, and clock signal continues triggering and connecting testing capacitor C _SWith reference capacitor C ₀Sensing module 12 produce two groups of TTL pulse trains, they convert Low Voltage Differential Signal to by sending module 13, are transferred to receiving end 2 by shielded cable.

Referring to Fig. 2, receiving end 2 comprises: a receiver module 21 and an output module 22; The Low Voltage Differential Signal that receiver module 21 will be transmitted by shielded cable by the sending module 13 of test side 1 is reduced to TTL pulse train, exports after being converted to analog voltage signal by output module 22 then, and their amplitude is proportional to testing capacitor C respectively _SAppearance value and reference capacitor C ₀The appearance value, can calculate described capacitor C after the quantification _SThe appearance value.

In the present embodiment, the signal generating module 11 of test side 1 is frequency and the fixing square-wave oscillator circuit of dutycycle that is made of monolithic low-pressure industrial level 555 timer U1, sensing module 12 is the monostable multiplex circuits that are made of two one shot multivibrator U2A of low pressure and U2B, and sending module 13 is the signaling conversion circuits that are made of two LVDS transmitter U3A and U3B.

During work, in test side 1, the 555 timer U1 output cycles of signal generating module 11 are t _SClock signal S, in order to trigger two one shot multivibrator U2A of low pressure and U2B.Connecting testing capacitor C on the low pressure one shot multivibrator U2A _S, connecting reference capacitor C on the low pressure one shot multivibrator U2B ₀Low pressure one shot multivibrator U2A and U2B produce TTL pulse train T respectively under the lasting triggering of clock signal S ₁With T ₂, its pulsewidth t ₁With t ₂Be proportional to testing capacitor C respectively _SAppearance value and reference capacitor C ₀The appearance value, referring to Fig. 3.

Testing capacitor C _SWith reference capacitor C ₀Each self-corresponding TTL pulse train T ₁With T ₂Be converted to Low Voltage Differential Signal by two LVDS transmitter U3A and U3B and be transferred to receiving end 2.

Comprise a pair of 3.3V power lead that attracts from receiving end 2 in the terminals, be used for being 555 timer U1 in the test side 1, the two one shot multivibrator U2A of low pressure and U2B and LVDS transmitter U3A and U3B power supply; Two one shot multivibrator U2A of the low pressure of selecting for use and U2B are integrated in the Chip Packaging, and two LVDS transmitter U3A and U3B are integrated in the Chip Packaging.

In the present embodiment, the receiver module 21 of receiving end 2 is the change-over circuits that are made of two LVDS receiver U4A, U4B, and output module 22 is by resistance R _f, R _S, capacitor C _fThe RC filtering circuit that constitutes.

During work, in receiving end 2, LVDS receiver U4A, U4B transmit test side 1 by shielded cable Low Voltage Differential Signal is reduced to TTL pulse train T ₁With T ₂, they convert DC simulation voltage signal A to by modular converter 22 then ₁, A ₂Output (V _HBe TTL high level amplitude):

$A_1=V_H\·\frac{t_1}{t_S}\·\frac{R_S}{R_f+R_S}$

$A_2=V_H\·\frac{t_2}{t_S}\·\frac{R_S}{R_f+R_S}$

D. c. voltage signal A ₁With A ₂The difference of amplitude is proportional to the survey capacitor C of institute _SThe appearance value, can predict C after the quantification _SThe appearance value.

Comprise a pair of 3.3V power lead in the terminals of connection receiver module 21, being used for is two LVDS receiver U4A and U4B power supply; Two LVDS receiver U4A and U4B are integrated in the Chip Packaging.

Shielded cable (not illustrating in the drawings) comprises a pair of 3.3V power lead and two pairs of Low Voltage Differential Signal lines (each detecting unit) of guiding test side 1 from receiving end 2 into.

The gain of the related device of the utility model or analog voltage signal A ₁Amplitude or A ₁With A ₂The difference of amplitude can do combination adjustment by the resistor and the capacitor parameters size that change the frequency of decision clock signal S in resistor R in the sensing module 12 and the signal generating module 11.

When device of the present utility model is used to the little capacitance detecting of pico farad magnitude, for improving the linearity of output module 22 output direct current signals to little electric capacity response, reduce the influence of pulse rise and fall fringe time width and stray capacitance simultaneously, at the testing capacitor C of sensing module 12 connections _STwo ends offset capacitor device in parallel, its appearance value and reference capacitor C ₀Equate (as the NPO level capacitor of 150pF), thereby make the TTL pulse train T of sensing module 12 outputs ₁The pulsewidth t of output ₁Be proportional to C _SAnd C ₀Appearance value sum, receiving end 2 is constant, referring to Fig. 4.Wherein, C ₀The appearance value must be enough greatly, make the two-way d. c. voltage signal A of output ₁, A ₂The difference of amplitude and C _SThe appearance value in the gamut scope, keep enough good linear relationship.

The dynamic range of the capacitance detecting of the related device of the utility model can be by resistor R, the reference capacitor C in the monostable multiplex circuit that changes sensing module 12 ₀And the resistor and the capacitor parameters size of the frequency of decision clock signal S done combination adjustment in signal generating module 11, must guarantee during adjustment that the cycle of the clock signal S that described signal generation module 11 produces is not less than C _SThe appearance value detects the maximum pulse width of the TTL pulse of pairing described sensing module 12 outputs of dynamic range headroom, i.e. t ₁＜t _S

When device of the present utility model is used to the test side occasions with limited space, signal generation module 11, sensing module 12 and sending module 13 are integrated in the shield as test side 1, receiver module 21 and output module 22 are integrated in another shield as receiving end 2, the Low Voltage Differential Signal of test side 1 output is transferred to receiving end 2 by shielded cable, therebetween stube cable, R that receiving end connects _T1And R _T2And the requirement of satisfying impedance matching between the connector.

Ultimate principle of the present utility model and principal character and technical advantage have more than been described.The technician of the industry should understand; the utility model is not restricted to the described embodiments; the foregoing description and instructions are only described principle of the present utility model; under the prerequisite that does not break away from the utility model spirit and scope; the utility model also has various changes and modifications; these changes and improvements all fall in claimed the utility model scope, and the protection domain that the utility model requires is defined by appending claims and equivalent thereof.

Claims (5)

1, a kind of device that is used for little capacitive transducer signal condition or capacitance detecting is characterized in that it comprises:

Produce two groups of pulsewidths by the oscillatory circuit that connects testing capacitor and be proportional to the pulse train of appearance value of the appearance value of testing capacitor and reference capacitor and the test side that sends respectively;

Receive described pulse train and be converted to the analog voltage signal that amplitude is proportional to the pulse train pulsewidth, can draw the receiving end of the appearance value of described capacitor after the quantification.

2, device as claimed in claim 1 is characterized in that: described test side is converted to Low Voltage Differential Signal with described pulse train and is transferred to described receiving end.

3, device as claimed in claim 1 is characterized in that: described test side is connected communication by shielded cable with described receiving end.

4, device as claimed in claim 1 is characterized in that, described test side comprises:

A signal generating module that is used to produce clock signal;

A sensing module that produces TTL pulse train by described clock signal, testing capacitor and reference capacitor;

And the TTL pulse train that described sensing module is produced is converted to the sending module that Low Voltage Differential Signal is beneficial to long-distance transmissions.

5, device as claimed in claim 1 is characterized in that, described receiving end comprises:

A receiver module that described Low Voltage Differential Signal is reduced to TTL pulse train;

And output module that described TTL pulse train is converted to analog voltage signal.

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