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The Design of Low-power Wireless Neural Signal Acquisition Module
Electronic Science and Technology
2019, 32 (1):
16-20.
DOI: 10.16180/j.cnki.issn1007-7820.2019.01.004
In this paper, RF radio frequency principle is used to design a pure analog low power wireless neural signal acquisition module suitable for small animals. Compared with digital-analog hybrid scheme, the pure analog implementation had the advantages of small size, low power consumption and simple structure. The acquisition module were divided into two parts including analog front-end amplification and wireless data transmission. With the use of low-power, low-noise instrumentation amplifier INA333 and OPA333 op amp analog front-end amplifier, a two-stage amplifier structure was formed and the power consumption and size of the circuit was reduced. The feedback enhancement effect achieved by adding a feedback inductor reduced the power consumption of the Colpitts oscillator. The FM modulation of the oscillator used the inter-polar capacitance of the transistor to form a pure analog wireless data transmission circuit, so that the acquisition module had the advantages of small size, low power consumption and wireless data transmission features. Circuit simulation and experimental test results both showed that the module could complete the wireless acquisition of animal neural signals and had a certain practicality.
Figure 4.
Low power colpitts oscillator
(a)Circuit diagram(b)Small signal equivalent model
Extracts from the Article
Colpitts振荡器由于结构简单,且具有良好的相位噪声性能,在短距离通信的低功耗系统中得到广泛引用[7,8,9]。本文基于Colpitts结构采用低噪声射频三极管MMBR941作为有源器件设计了一款工作在433 MHz的低功耗振荡器,如图4所示。
如图4(a)所示,Colpitts振荡器工作时,由三极管T与外围反馈环路(C10与C11)构成的正反馈结构产生负电导,其产生的能量补偿负载电导的能量消耗[10]。本文通过在三极管基极添加反馈电感Lg加深了正反馈结构的反馈深度[11],使振荡器可以在更低的静态电流条件下起振工作,从而降低了振荡器的功耗。根据图4(b)得到振荡器起振条件应为[12,13]
由图4可以求得各个参数
根据PN结势垒电容容值随着外加反偏电压变化的特性,本文利用三极管中bc结的寄生二极管作为变容二极管,实现FM调制,不需要额外添加变容二极管,减少了电路元件数,缩小了系统尺寸。根据图4(a)所示电路,可以得到如图5所示的振荡电路的LC振荡环路。
对图4(a)所示电路图进行仿真得到如图8所示的输出频率关于调制电压的变化曲线。调制电压添加在三极管基极,因此,调制电压越大,三极管的bc结反偏电压将越小,导致其势垒电容将越大,振荡频率越低。
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