Design And Implementation Of CFOA-based Fast Response Filter

We extract the signal of rat brain cortex that is a kind of electric signal, through research the fluctuation of voltage signal is used to study the pathological changes of the rat brain in the system of multi-channel data acquisition system, through the simulation to study the little mouse changes in order to further study the brain cortex provides solid material, such as treatment for epilepsy, lead to make great contributions to the pathological changes in advance can prevent the occurrence of diseases such as epilepsy, but the eeg is a very small voltage amplitude of the signal, its narrow frequency range, which make it particularly vulnerable to the special biological signal noise interference and acquisition, so the filter circuit is very important. Filter is a kind of can filter the signal mixed some noise in electronic devices, the filter band, we don't need leave the band we need. Filter research increasingly mature, but now the active filter is usually used type voltage Feedback operational Amplifier(voltage Feedback the operational Amplifier,VFOA). Although VFOA has many advantages, but its existence mode of voltage amplifier, the common disadvantages of practical circuit in order to reduce the impact of a large number of high impedance nodes, with lower current consumption, and enhance voltage swing method,therefore in the process of high frequency and high speed signal ability significantly decreased.We can use the Current mode Amplifier instead of voltage Amplifier to solve the problems, we often use in the Current mode Amplifier current-mode operational Amplifier(Current Feedback the operational Amplifier, CFOA); It has: in phase as the high impedance, inverting the basic is zero, little change when change the gain bandwidth, pressure swing rate is very fast, waveform fluctuations and distortion will be lower, in we collect the feedback resistance will limit its value.Here are commonly used in the filter circuit CFOA is cross resistance type operational amplifier,in a closed loop system, if any feedback, the feedback is current, the amount of current through inverting the input voltage and who enter the interior of the CFOA, and in the open loop system,the gain of the dimension is expressed through cross resistance, and our common, compared to the traditional pattern of voltage operational amplifier is VFOA topological structure and working principle of different brings obvious advantages, solve the problem of the traditionalmodel of voltage circuit, with obvious dynamic characteristics, the fine rate of pressure swing and rapid response, the most practical advantages, can other circuit structure theory to prove it,not only occupy the important position in the filter circuit, in some basic circuit is superior to other VFOA circuit, occupies an important ratio in the integrated electronics, is now the focus of integrated op-amp.CFOA is applied to filter circuit is mainly studied and designed the second-order filter circuit, and presents a general circuit structure of section n filter circuit, break through the traditional VFOA filter circuit faults of the high-speed signal processing ability and signal distortion easily, it has advantages of excellent performance and good dynamic characteristics,design of filter press place good rate, low delay time, waveform distortion, noise resistance due to VFOA circuit, multi-channel data acquisition system in our laboratory and pathological tissue processing has been widely used in the system. Article is put forward based on the rapid response of the CFOA low-pass filter, the design method of the multi-channel data acquisition system of multi-channel analog signals have a low-pass filter can be Shared by analog switch, so as to simplify the circuit design, this design by simulation validation and strap test, have reached the design requirements.In the process of filtering noise, low pass filter is often the key to affect acquisition precision and speed, this paper proposes a fast response based on current feedback amplifier design method based on low-pass filter, the Multisim simulation and actual strap test, the impulse response delay time than the low pass filter based on voltage operational amplifier design lost about 1 to 2 orders of magnitude, thus proving the effectiveness of the proposed method, a similar method can be used to implement the design of other types of filters.In this paper, the second part from the beginning of the CFOA internal topology, describes the basic structure model and the implementation of specific functions, internal working parameters of the CFOA, by comparing the CFOA and VFOA function, the advantages of using CFOA, avoid VFOA circuit faults, by calculating the transfer function of the network structure,the theoretical n order filter design, design circuit diagrams were obtained through the operationin the laboratory, by testing the simulation software of measurement and strap, obtain the result of the experiment, with the measured results compare analysis, verify the advantage of the filter in this paper. And passes through the filter circuit theory analysis, and by studying the traditional circuit type filter and reference filter paper, this article third part to three circuit is the comparison of experimental data, through this kind of filter with the traditional filter circuit and a new type of filter circuit, through experiment data found circuit of advantages, this paper summarize the last part of the filter.