What are the best practices for ensuring CMOS analog and mixed-signal circuits meet industry standards?

1 Choose the right topology

The first step in designing CMOS analog and mixed-signal circuits is to choose the right topology for your application. The topology is the basic structure of the circuit, such as the number and type of transistors, resistors, capacitors, and feedback loops. The topology determines the main characteristics of the circuit, such as gain, bandwidth, linearity, noise, and stability. You should choose a topology that meets your specifications and minimizes the trade-offs between these characteristics. For example, if you need a high-gain amplifier, you might use a cascode topology, which stacks two transistors to increase the output resistance and the gain. However, this also increases the power consumption and the parasitic capacitance, which might affect the bandwidth and the speed of the circuit.

3 Model and simulate the circuit

The third step in designing CMOS analog and mixed-signal circuits is to model and simulate the circuit using software tools. The modeling refers to the representation of the circuit components and their behavior using mathematical equations or physical parameters. The simulation refers to the analysis of the circuit response to different inputs, outputs, and conditions using numerical methods or algorithms. You should model and simulate the circuit to verify the functionality and performance of the circuit and to identify and correct any errors or issues. For example, if you want to check the stability of the amplifier, you might use a small-signal model to calculate the poles and zeros of the transfer function and a transient analysis to observe the step response of the circuit.

4 Consider the layout and parasitics

The fourth step in designing CMOS analog and mixed-signal circuits is to consider the layout and parasitics of the circuit. The layout refers to the physical arrangement of the circuit components and their interconnections on the chip. The parasitics refer to the unwanted effects of the layout, such as the resistance, capacitance, and inductance of the wires and the devices. You should consider the layout and parasitics of the circuit to ensure that they do not degrade the performance or functionality of the circuit and to optimize the area and the power consumption of the chip. For example, if you want to minimize the mismatch of the transistors, you might use a common-centroid layout, which distributes the transistors symmetrically around a center point and cancels out the gradients of the process parameters.

5 Test and calibrate the circuit

The final step in designing CMOS analog and mixed-signal circuits is to test and calibrate the circuit using hardware tools. The testing refers to the measurement of the circuit output and performance using instruments, such as oscilloscopes, multimeters, and spectrum analyzers. The calibration refers to the adjustment of the circuit parameters or components using techniques, such as trimming, tuning, or compensation. You should test and calibrate the circuit to ensure that it meets the industry standards and the specifications and to compensate for any deviations or variations caused by the process, the temperature, or the aging. For example, if you want to improve the accuracy of the converter, you might use a digital-to-analog converter (DAC) to generate a reference voltage and a comparator to compare the input and the output voltages and to correct any errors.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?