A CPLD piezoelectric biosensor detection circuit design (1)

This article describes an approach based on complex programmable logic devices (CPLD) of piezoelectric biological sensor detection circuit. the detection circuit for high-performance CPLD (MAX7128) as the core, the realization of a piezoelectric biosensor 10MHz high frequency signal measurement and collection, as well as the acquisition of frequency data dynamic, real-time display and frequency data serial communication function of the circuit-small volume, high integration, real-time performance with high reliability, high characteristic. in addition, the system can also be via RS-232 serial interface with computer connection for data transport and data storage and analysis-elaborated system overall structure design and implementation of the system hardware parts, and gives the CPLD core simulation result and data acquisition software measurement frequency curve.

Domestic and overseas based on piezoelectric quartz crystal microbalance technology detection instruments most used to design the oscillation circuit box, use the frequency of the high-resolution counter measurement frequency output, then a scheduled equipment manual count, complex, automated low-micro piezoelectric biosensor detection circuit adopts the most promising complex programmable logic devices (CPLD) as the core device designed. currently, CPLD integration can reach 25 million equivalent gate, working speed up to 180MHz. it with a high degree of automation of the kernel program development tools that can greatly reduce the system's cycle, and data collection can be done by a CPLD chips, system-wide scale significantly reduce hardware-in system development phase, because the CPLD pin more flexible, erasable programmable capacity, thus making modifications to the original design, you only need to modify the original design documents and then on the CPLD chip reprogramming to, and does not need to modify the circuit layout, much less need to rework the printed circuit board, this greatly improves the system's flexibility. combination of piezoelectric properties of bio-sensor, a micro Piezoelectric sensor detection circuit has a very important significance.

1 principle of piezoelectric biosensor

Piezoelectric quartz crystal frequency shift Δ F and uniform adsorption on the surface of the lens of a very thin layer on a rigid material quality Δ relationship between proportional m, Sauerbrey equation describes, and is AT the cutting of quartz crystal, can get Sauerbrey equation:

In the formula, Δ F, Fq (Crystal base frequency), Δ m, A unit Hz Hz, respectively, g.cm-2, cm2. quartz oscillation in the gas phase, Δ Δ f and m is a simple linear relationship, so the quartz can be used to do very sensitive quality checker, its detection limit can reach ng level (10-9g.cm-2), or even pg (10-12g.cm2) level.

Based on piezoelectric quartz crystal sensor principle designed a micro Piezoelectric sensor detection circuit, its detection principle as fixed in advance on the sensor and the matter can be measured and reaction in the "probe", detection test of time, along with affinity reaction, detection circuit real-time tracking response process, record sensor quality changes in the frequency change, and then pass the above quantitative relation calculation of quantity to be measured, its sensitivity to NACO level, combined with gold nanoparticles technology sensor sensitivity improvement for 3 ~ 5 times.

2 circuit hardware design

Micro Piezoelectric sensor detection circuit is the result of the previous generation of instrument development experience and improved basis.

It abandoned previous TTL IC or MCS as core circuit fluctuation, poor stability, circuit board drawing complex, is not conducive to the disadvantage of upgrading, select the use of ALTERA Corporation production complex programmable logic devices (CPLD) MAX7128 as the core, are based on the RS232 communication serial interface data acquisition and analysis platform. the system is divided into seven modules: power supply module, RS-232 level translation module, oscillation circuit module, clock module, digital display module, MAX7128 kernel module circuit board layout. circuit shown in Figure 1.

Figure 1 hardware chart

Figure 1, the USB port for piezoelectric biosensor and detection circuit connected to the interface; RS-232 estuary and the computer connected to the interface, the digital sensor signal (frequency value) on a computer, a computer (PC) sensor signal real-time acquisition and display that data collection program is written in VC ++ 6.0; work to provide system OSC1 clock oscillation circuit, the TTL chips and 12MHz standard Crystal composition, producing 1s pulse signal, as the CPLD working clock input, RS-232 communicate timing pulse and digital tube dynamic display timing pulse, accuracy is high, and accurate; OSC2 oscillator circuit for sensor, after several generations of repeatedly modified, in gas, liquid are normal oscillation and waveform normal, the sensor surface reaction signal into pulse signal, enter the CPLD to signal data acquisition; digital display cathode with a total of 8 × 8 led, dynamic scanning display current sensor signal values and simple data analysis results; provides DC power to the system operating voltage 5V DC, contains 6 ~ 5V regulator 15V into; RS-232 level conversion circuit from CPLD output CMOS level into computer accepted TTL level, but also to increase the data transmission distance.

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