Transcript
ECEN4827/5827 Analog IC Design Problem D.2. Design of a bandgap reference
In this problem, the objective is to design the bandgap reference circuit shown in Fig.1 using the 0.35u CMOS process. The supply voltage is VDD = 3.3 V. The transistor aspect ratios W/L (in um/um) and the diode (WDIODE) area scale factors are shown in Fig. 1. RPN resistors R1 and R2 are used in the circuit. +VDD 10/5 M3
I3
10/5
10/5
M4
M5
I4
I5 Vref
M1
M2 5/5
5/5
R1 RPN W=1u D1
D2
n=1
n=8
R2 D3 n=1
Figure 1 Bandgap reference in 0.35u CMOS process. (a) Find R1 and LR1 (the length of R1 resistor) so that current I5 equals approximately 5 µA at room temperature (27oC, or 300oK). LR1 can be changed in 1u increments. Show hand calculations and the result of verification by simulation (based on the simulation results, adjust LR1 if necessary). For the selected LR1, find the temperature coefficient TCF(I5) at room temperature (by hand calculation). (b) Find R2 and LR2 (the length of R2 resistor) so that TCF(VREF) equals approximately 0 at room temperature. The best design approach is to first find the required resistance approximately, by hand calculation. Then, a parametric sweep over LR2 as the parameter can be used to find the best value for LR2. The length of LR2 can be changed in 1u increments. For the selected LR1 and LR2, what is VREF at room temperature? How much does the reference voltage VREF vary over the range from –50oC to +100oC? Turn in a plot of VREF as a function of temperature. Extra credit (worth 50% of the points assigned to this problem, no partial credit will be given): modify the circuit in Fig. 1 so that a bandgap reference voltage Vref having approximately zero temperature coefficient at room temperature is obtained using only two diodes (D1 and D2). Turn in your complete LTspice schematic, hand calculations showing how you selected parameter values, and a plot of Vref as a function of temperature (–50oC to +100oC).
