Example CMOS Folded Cascode Circuit for LTSpice Simulation

a182240 wrote:

Can you give me an example CMOS folded cascode circuit for me to simulate in LTSpice ?

Hello,

I can provide you with a basic CMOS folded cascode amplifier circuit that you can simulate in LTSpice. Below is a detailed description of the circuit, along with the necessary steps to set it up in LTSpice.

Circuit Description:

A CMOS folded cascode amplifier typically consists of the following components:
1. Differential Input Pair: NMOS transistors (M1, M2) form the differential input stage.
2. Current Source: A current source (M5) biases the differential pair.
3. Folded Cascode Stage: PMOS transistors (M3, M4) and NMOS transistors (M6, M7) form the folded cascode stage.
4. Current Mirrors: Used for biasing and mirroring currents.
5. Load Resistor: Connected to the output to represent the load impedance.

Schematic:

Below is a simplified schematic of a CMOS folded cascode amplifier:



LTSpice Netlist:

Here is an example netlist for the CMOS folded cascode amplifier:



Explanation:

1. Transistor Models:
- NMOS: Typical NMOS transistor with a threshold voltage of 0.7V.
- PMOS: Typical PMOS transistor with a threshold voltage of -0.7V.

2. Current Source (ISS):
- Provides a constant current for the differential pair. Here, we assume 100µA.

3. Differential Pair (M1, M2):
- The input stage comprising two NMOS transistors forming the differential amplifier.

4. Cascode Transistors (M3, M4):
- Folded cascode transistors that provide high output impedance and gain.

5. Load Resistor (RD):
- Provides a load for the cascode amplifier. Here, we assume a 10kΩ resistor.

6. Biasing current mirrors (M5, M6, M7, M8):
- Transistors to properly set the currents in the folded cascode stage.

7. Simulation Command:
- Runs a transient analysis to simulate the behavior of the circuit over time.

Steps to Simulate in LTSpice:

1. Create New Schematic:
- Open LTSpice and create a new schematic file.
2. Add Components and Netlist:
- Add NMOS and PMOS transistors, resistors, voltage sources, and wire them as described based on the provided netlist.
3. Add the Model Definitions:
- Define NMOS and PMOS models either in the schematic or in a separate .mod file.
4. Run Simulation:
- Use the provided simulation command to perform transient analysis.

This netlist and schematic should help you get started with simulating a basic CMOS folded cascode in LTSpice. You can further tweak the transistor dimensions, currents, and other parameters as per your specific design requirements.

Let me know if you need further assistance or have any specific questions.