## 4 Proposed C2V with Application of Fuzzifier Circuit  
As we know in the Fuzzifier part of the FLC, the Fuzzifier circuit is used to make the antecedents as Fuzzy currents. Hence we used the proposed Fuzzifier circuit here to convert the output signal of sensed blood glucose data to Fuzzy language terms. According to Figure 12, we previously worked on a MEMS glucose microsensor [8] which sensed the blood glucose in milli mole to capacitance variations. Thus we proposed a new circuit of capacitance to voltage (C2V) convertor as a bridge between MEMS microsensor and Fuzzifier circuit. The proposed C2V circuit is shown in Figure 13 with the following details:  
* \(Cx\) is the variable capacitor which is achieved (in range of 62\(\sim\)380 fF) using MEMS glucose microsensor [8] with taking a sample of blood glucose (of 1\(\sim\)20 mM). * \(C_{in}\) is the parasitic and Op-Amp input transistor (\(W/L=10/2\)) capacitor which is equal to \(\sim\)40 fF. * \(C_{f}\) is the feedback capacitor with size of transistor \(W/L=25/10\) which is equal \(\sim 1\)pF (Figure 13b). * \(C_{L}\) is the load capacitor plus \(C_{gs}\) of next stage transistors (Fuzzifier input). Figure 11: Triangular membership functions with setting minimum voltage reference and high digital data. Figure 12: Intelligent sensing blood glucose and insulin injection system using MEMS Microsensor, CMOS FLC and MEMS micropump or (Sensing, Fuzzy Processing and Injecting system) [8]. In the circuit of Figure 13a and using switched capacitor properties, the sampling and amplification mode are achieved using two clocks of ck1 and ck2 as follow:  
When ck2 is in high level, _Cf_ is discharged via Feedback switch. In this situation, ck1 is in low levels and causes to charge _Cx_ via PMOS transistor of invertor. Thus sampling mode is completed. Unlike the previous case, when ck2 and ck1 are in low and high levels respectively, then the amplification mod is completed. In this situation and writing KCL in node x, the voltage _Vout_ is achieved by Equations (6) and (7):  
\[(V_{out}-V_{x})C_{f}s=V_{x}C_{in}s+(V_{x}-V_{in})C_{x}s \tag{6}\]  
On the other hand, \(V_{out}=-A_{v}/V_{x}\) thus we will have:  
\[V_{out}=V_{in}\times\frac{C_{x}}{C_{f}}(1-\frac{C_{f}+C_{x}+C_{in}}{C_{in}} \frac{1}{A_{v}}) \tag{7}\]  
It shows that the output voltage of _Vout_ is a function of _Cx_ in amplification mode. Thus the minimum op-amp gain which should guarantee gain error of 0.01%, will be obtained according Equation (8):  
\[\frac{C_{f}+C_{x}+C_{in}}{C_{in}}\frac{1}{A_{v}}=0.01\%=10^{-4}\Rightarrow \frac{1000f+380f+40f}{1000f}\frac{1}{A_{v}}=10^{-4}\Rightarrow A_{v}=1.42 \times 10^{4}=83 dB \tag{8}\]  
Given the low rate of glucose changes, so according to Figure 14 we used two-stage op-amp to have high swing and more accuracy. Simulation results of Figure 15 show the DC gain of \(\sim\)83 dB and phase margin of 56\({}^{\circ}\) which validate Equation (8) and our purpose in the C2V circuit of Figure 13. Now we apply variable capacitor of _Cx_ (in range of 62-380 fF) to the proposed C2V circuit. According to Figure 16 simulation results show that the output voltage of _Vout_ is obtained in range of 0.6-2 V. Figure 17 shows a suitable linearity of voltage _versus_ produced capacitance of MEMS glucose microsensor. The proposed C2V circuit is simpler, has a lower die area, and lower power in comparison to previous works [14,15]. Figure 16: Simulation results of C2V convertor (blood glucose data (capacitance) to voltage of 0.6\(\sim\)2 V). Figure 14: Two stage op-amp which designed and used in C2V circuit of Figure 13.  
Figure 15: Simulation results of two-stage op-amp: (**a**) DC gain of \(\sim\)83 dB; (**b**) phase margin of 56\({}^{\circ}\). The systematic model of Fuzzifier (from Figure 12) is evaluated with applying an input which obtained four Fuzzy language terms using Matlab software (Figure 18).