// VerilogA for photodiode, photo_SPICE, veriloga

`include "constants.vams"
`include "disciplines.vams"

module photo_SPICE(Anode,Cathode,Light);
	inout Anode, Cathode,Light;
	electrical Anode, Cathode,Light;


		//In m
		parameter real xph=1e-6;
		parameter real xjm=1e-6;
		// In cm
		parameter real xphi=1e-4;
		parameter real xj=1e-4;
		parameter real xW=50e-4;


		//Transmition coefficient
		parameter real Tx=0.5;

		//Semicondutor parameters
		parameter real Na=1.3e15;
		parameter real Nam=1.3e21;
		parameter real Nd=1.0e20;
		parameter real Ndm=1.0e26;
		parameter real ni=9.65e9;
		parameter real nim=9.65e15;
		// h+, e- lifetime
		parameter real ton=200e-6;
		parameter real top=0.2e-6;
		//h+ diffusion coefficient in cm2/s
		parameter real Dp=12;
		//e- diffusion coefficient in cm2/s
		parameter real Dn=36;
		// Surface recombination in cm/s
		parameter real Sp=10;
		parameter real Sn=4e4;
		//Relative dielectric coefficient of silicon
		parameter real Ks=11.8;

		
		//Necessary parameters
		parameter real h=6.6260696957e-34;
		parameter real c=3.0e8;
		parameter real lambda = 500e-9;
		parameter real T=298.0;
		parameter real er=12.0; 
		parameter real eo=8.854187817e-12;
		parameter real k=1.3806488e-23;
		//e- charge
		parameter real q=1.60217657e-19;

		//Photodiode emission coefficient
		parameter real N=1.35;
		//Reverse bias saturation current
		parameter real Is=1e-14;
		//Dark current equivalent resitance
		parameter real Rdark=1e8;


		parameter real alpha=760;


		//Variables
		real phio,Area,mu,En,Vbi,W,Wcm,Vt;
		real pno,npo,Ln,Lp;
		real kp,kn;
		real AA,BB,CC,DD,EE,FF,GG,HH,II,JJ,KK,LL,MM,NN;
		real OO,PP,QQ,RR,SS,TT,UU,VV,WW;
		real C1, C2, C3, C4,Cpd;
		real A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11;
		real B1, B2, B3, B4, B5, B6, B7, B8, B9, B10, B11;
		real Iaa,Id,Icpd;
		real H1, H2;
		real jpsub,jndop,jdepl;
		real Popt;
		real Vbias;
	
	
	branch (Anode,Cathode) b1;
	
	analog begin


			Popt=V(Light);	
			
			//Depletion width
			Vt=k*T/q;
			Id=Is*(exp((-V(b1))/(N*$vt))-1);
			Vbi=Vt*ln((Na*Nd)/(ni*ni));
			W=sqrt((Vbi+V(b1))*(1.0/Ndm+1.0/Nam)*(eo*er)/q);
			Wcm=W*100;

			//Depletion capacitance calculation
			GG=(Ks*eo)/(W);
			HH=xph*xph;
			Cpd=GG*HH;
			Icpd=Cpd*ddt(V(b1));
			//

			//Phi0 and Absorption lengths
			En=(h*c)/(lambda);
			npo=Ndm;
			pno=(nim*nim)/Ndm;	
			Ln=sqrt(Dn*ton);
			Lp=sqrt(Dp*top);		

			phio=(Popt*Tx)/(En*10000);
			kp=(phio*alpha*top)/(1-alpha*alpha*Lp*Lp);
			kn=(phio*alpha*ton)/(1-alpha*alpha*Ln*Ln);
		
			//Jndop 
			
			A1=alpha*Ln+(Sn*Ln)/Dn;
			A2=1+(Sn*Ln)/Dn;
			A3=1-(Sn*Ln)/Dn;
			
			H1=A1/A2;
			H2=A3/A2;
			
			A4=(H1*(exp(xj/Ln)))/H2;
			A5=exp((-xj)/Ln);
			A6=(exp(xj/Ln))/H2;
			A7=exp((-alpha)*xj);
			
			C3=((-kn)*(A7+A4))/(A5+A6);

			A8=H1*(exp((-xj)/Ln));
			A9=H2*(exp((-xj)/Ln));
			A10=exp(xj/Ln);
			A11=exp((-alpha)*xj);
	
	
			C4=((-kn)*(A11-A8))/(A10+A9);
			
			AA=(-kn)*alpha*(exp((-alpha)*xj));
			BB=(C3*(exp((-xj)/Ln)))/(Ln);
			CC=(C4*(exp(xj/Ln)))/(Ln);
			
			jndop=q*Dn*(AA-BB+CC);

			
			//Jpsub
			B1=alpha*Lp-(Sp*Lp)/Dp;
			B2=1+(Sp*Lp)/Dp;
			B3=1-(Sp*Lp)/Dp;
			
			B4=kp*(exp((-alpha)*(xj+Wcm)))*(exp(-(xj+Wcm)/Lp));
			B5=kp*(exp((-xW)*(alpha+1/Lp)));
			B6=exp(((-2)*xW)/Lp);
			B7=exp(((-2)*(xj+Wcm))/Lp);

			C1=((-B4)*B2+(-B1)*B5)/(B6*B3+B7*B2);

			
			B8=kp*(exp((-alpha)*(xj+Wcm)))*(exp((xj+Wcm)/Lp));
			B9=kp*(exp((-xW)*(alpha-1/Lp)));
			B10=exp((2*xW)/Lp);
			B11=exp((2*(xj+Wcm))/Lp);


			C2=((-B8)*B3+B9*B1)/(B11*B3+B10*B2);

			DD=(-kp)*alpha*(exp((-alpha)*(xj+Wcm)));
			EE=(C1*(exp((-(xj+Wcm))/Lp)))/(Lp);
			FF=(C2*(exp((xj+Wcm)/Lp)))/(Lp);
			
			jpsub=q*Dp*(DD-EE+FF);


			//Jdepl			

			jdepl=q*phio*(exp(-alpha*xj))*(1-(exp(-alpha*Wcm)));
			
			// Photogenerated current
			Iaa=xphi*xphi*(jpsub+jdepl+jndop);			

		
	I(b1)<+ Iaa;
	I(b1)<+ -Id;
	I(b1)<+ -V(b1)/Rdark;
	I(b1)<+ -Icpd;
	end

endmodule