Components*

Note that g_m is in μA/V.

^*Run the first part of Procedure with GainNMOS.vi, below, without the capacitor, to obtain V_effn and bias I_D, for computing g_m.

LabVIEW Computations

Parameters: V_tno, k_n

Procedure (Obtain Parameters and Bias Variables)

• Open GainNMOS.vi. Install your R_S value. Without the capacitor installed, set the Mode Switch to Param (red, switch in logic state 0). Run the VI for a VDD sweep to get the parameters. (Note: The sweep rate is configured to be slow in case the capacitor is in place during the sweep.) The VDD sweep is from 4 V to 10 V. Obtain a log of the results.
  
  

Procedure (Gain Measurement)

• In the Param mode, the VI finds and indicates VDDbias corresponding to the optimum V_DS = (V_DD – V_Rs + V_effn)/2. This permits maximum signal swing without distortion. Set the indicated value of VDDbias into the Set VDD Digital Control. Run the VI with the Mode Switch set to Gain (green, switch position logic 1) without the capacitor. Obtain a log of the Front Panel. Default and save the Front Panel.
  
  
• At the end of the parameter sweep, Veffn is indicated for VDDbias. The value is retained in the Digital Indicator in the gain measurement. The value of ID indicated in the gain measurement is the amplifier gain bias value. Use Veffn along with bias ID, to compute g_m and thus C_s. Use Project07.mcd for the calculation.
  
  
• Install the capacitor. Make certain that the polarity of the capacitor is correct. Check that the Mode Switch is set to Gain (switch position logic 1). Check that the value of VDDbias matches the value in Set VDD Digital Control. The VI will measure the gain at this one VDD setting (optimum for distortion-free output). The signal frequency is initially 500 Hz.
  
  
• Run the VI and vary the value of Vs to determine that the gain result, V_d/V_g, is not affected by changes, that is, by distortion. Default and save the Front Panel. Obtain a log of the results. Also, run with slight variations in Freq (e.g., 300 Hz). Note that the parameter values are preserved when running the gain mode. Parameter, bias variable, and gain data are required for the project Mathcad file.