11. 11
AC Analysis on Common-Gate Amplifier with Active
Load
A(dB) = 40.5dB
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QUESTION 1
What is the difference between the characteristics of the CG amplifier and the CS amplifier?
Common-Source Amplifier Common-Gate Amplifier
Moderate Voltage Gain
Large Current Gain
High Input Impedance
Low Output Impedance
High Voltage Gain
Low Current Gain
Low Input Impedance
High Output Impedance
A(dB) = 40.5dB
AC and DC Analysis on Common-Source
Amplifier with Current Source Load
AC and DC Analysis on Common-Gate
Amplifier with Current Source Load
Notas del editor
The code in the left was used to simulate the circuit on the right. The resistor used has a value of 100kΩ and the W/L ratio of the NMOS is 2/1.
Vbias >= 1.235V Saturation
Vbias < 1.235V Cutoff
The bias voltage at the gate terminal was 1.235V because a lesser value than that will make the NMOS in the Cutoff state.
The gain for the circuit was 10.1dB with a gain bandwidth of 491kHz.
In step 2, it was tasked to change the value of the resistor on the circuit. The resistance was decreased by 100kΩ, 300kΩ, and 500kΩ in order. Other parameters were left unchanged.
The condition of the NMOS while varying the resistor on the drain is shown in the following tables.
The hand calculated gain was somewhat similar to the simulated gain. As the resistance was increased, gain also increases and the bandwidths are decreasing.
A current mirror was used in order to simulate a current source load in the common-gate amplifier. The MOSFETs used has a W/L ratio of 2/1. The bias current used was 1.2V.
VIN > 0.46V MP2 becomes linear
VIN < 0.45V MN1 becomes linear
To ensure that the MOSFETs are in the saturation region, the VIN used was 0.46V. A VIN greater than 0.46V will make the MP2 to operate in the linear region. A VIN lesser that 0.45V will operate the MN1 in the linear region.
The Vout starts to saturate when the VIN is around 0.6V.
The gain of the circuit reached to around 40.5dB with a gain bandwidth of around 2.12MHz.
