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Output Buffer: The output buffer is an inverter with IOH =1mA @ VOH=2.4V & IOL=12mA @ VOL=0.4V It has a 3 O/P states (0,1,Hi-Z). The O/P buffer is designed in VLSI with the following capabilities: 1. Meets IOL & VOL specs for all VDD ranges (4V-6V). 2. Meets IOH & VOH specs for all VDD. 3. Minimize transient power dissipation. 4. has Tf = & Tr= for CL = 50 PF. I. Design of output inverter: PMOS transistor sizing: VS = VB=VDD= 4V (worst case for VDD & no body effect). VD = VOH= 2.4V VG= 0V VTp=VTp0= -0.734 V So, VDS= -1.6V, VGS= -4V since VDS>VDSAT= -4 +0.734 = -3.266 then transistor operates in linear region. IDS= k’(W/L)p[(VGS-VTp)VDS - VDS²/2] Where k’= µpCOX where COX = e0er(SiO2) / TOX = (8.854 * 10 -12)(3.9)/(15.5 * 10-9)= 2.2278 * 10-3 F/m2 Then, k’= (160 * 10-4) COX = 3.5644 * 10-5 F/V.s (W/L)p=IDS/{k’[(VGS-VTp)VDS-VDS²/2]} =1.0*10-3/{k’[3.9456]}= 7.111 If we take Lp = min. Length = 0.8µ, Wp= 0.8 * 7.111= 5.69µ So (W/L)p = 5.69/0.8 NMOS transistor sizing: VS = VB= 0V (no body effect). VD = VOL= 0.4V VG= 4(worst case for VDD) VTn=VTn0= 0.844 V So, VDS= 0.4V, VGS= 4V since VDS
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