Analog VLSI-Laboratory Laboratory #4: Analysis and Design of Current Mirror Objective: To understand the fundamental operation of current mirror with different architecture. With real MOSFET device model, simulate the basic current mirror using using LTSpice and find out the performance parameter of the basic current mirror. Certain specs are given for the advanced current mirrors such as cascaded current mirror and low-voltage current mirrors. Then, the students are designing and simulating the relevant circuits. Task 1: Construct the basic current mirror with given schematic below R1 11 1p + V1 0.1m V2 C1 3.5 vcm M1 M2 1p SINEC AC 10 Test TestN model Test nmos (kp=90u vto=0.7 lambda=0.1) model TestP pmos (kp=40u vtO=-0.7 lambda=0.1) .op Figure 1. Schematic of basic current mirror The schematic given here has the following dimensions and designs. NMOS M1 and M2: L=1um, W=100um Reference Current Source: 0.1mA Resistor R1 is used for capturing the AC current through the current mirror output. 1. DC analysis Run the DC analysis and find the operating point for M1 and M2. 1.1. Given the bias condition in dc operating point simulation. Hand calculate the DC current through M1 and M2. 1.2. Calculate the lambda (A) parameters from the DC current through M1 and M2. Does it match the channel length modulation effect from the self-defined model? 2. AC analysis
Run the AC analysis from 1MHz to 1GHz with >20 number of points per decade. 2.1. Hand calculate the output Impedance of the current mirror device (M2). Then, compare the calculated output impedance from the simulated output impedance. 2.2. Change the current source from 0.1mA to 0.5mA. Then, find the output impedance of the current mirror device. What is the simulated output impedance? Does the output impedance change match your analysis/intuition? 2.3. Change the current source back to 0.1mA. Then, find the frequency where the output impedance is reduced by -3dB. Where is this frequency located? Please calculate the expected frequency from your hand-analysis.
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