To reduce, if not completely eliminate, signal interference, mixed-signal PCB design requires a fundamental grasp of analog and digital circuits. In order to maintain the signal integrity of the entire system, the components of a modern system must function in both the digital and analog domains.

PCB layout is a challenging step in the mixed-signal development process, and component placement is just the beginning. The layers of the board and how to effectively manage those layers must also be taken into account in order to reduce interference brought on by parasitic capacitances that can unintentionally form between layers between PCB planes.

A crucial component of the PCB layout design for mixed-signal systems is grounding. Even though the subject of grounding is frequently discussed in the business, engineers may find it challenging to come up with a consistent method. An difficulty with high-quality grounding, for instance, can have an impact on the layout of the entire high-performance mixed-signal PCB design. As a result, this factor should not be disregarded.

Ⅰ. Component placement

Before installing circuit components, a floor design for the system must be made, much like when building a house. This procedure should assist prevent high noise signal interference and establish the overall integrity of the system architecture.

It is advised, particularly for high-speed circuits, to follow the signal path shown on the schematic when creating a floor design. Another crucial component of the design is where the components are placed.

To decide where to put the system's components, designers should be able to recognize crucial functional blocks, signals, and linkages between blocks. For instance, it is desirable to locate connectors on the board's edge, while it is necessary to position auxiliary parts like decoupling capacitors and crystals as close as possible to mixed-signal devices.

Ⅱ. Separation of analog and digital modules

To minimize the common return path for analog and digital signals, consider analog and digital block separation so that analog signals do not mix with digital signals.

Figure 1. Analog and Digital Circuit Separation

Figure 1 shows a good example of the separation of analog and digital circuits. The following When dividing the analog and digital portions, it should be kept in mind:

It is advised to install delicate analog components in the analog plane, such as amplifiers and references. The opposite side/digital plane must be used for noisy digital components like logic control and timing blocks.

An analog-to-digital converter (ADC) or digital-to-analog converter (DAC) in the system that is mixed-signal and has a low digital current can be handled in a manner similar to how analog components are handled in the analog plane.

It is advised to separate the analog and digital power supply for designs with numerous high-current ADCs and DACs. In other words, DVDD should be connected to the digital part and AVCC must be attached to the analog part.

The space and heat produced by microprocessors and microcontrollers can be significant. For improved heat dissipation, these components must be positioned in the board's center and have to be near the circuit blocks that they are meant to be connected to.

Ⅲ. Power module

The power supply is a crucial component of the circuit and needs to be treated with care. Power modules must, as a general rule, be proximate to the components they power while being isolated from the rest of the circuit.

Dedicated power modules can be utilized for the analog and digital sections when devices in complicated systems have many power pins in order to prevent noisy digital interference.

To reduce inductance and prevent current limitation, power lines should be short, straight, and use wide traces.

Ⅳ. Decoupling technology

One of the crucial factors that designers must take into account in order to meet the system's desired performance is the Power Supply Rejection Ratio (PSRR). The performance of the device is ultimately determined by PSRR, which assesses the gadget's sensitivity to changes in the power supply.

Preventing high frequency energy from entering the device is required to maintain ideal PSRR. Using a mix of electrolytic and ceramic capacitors, the device power supply can be effectively isolated from a high impedance ground plane for this purpose.

A low noise environment is what effective decoupling is meant to achieve for circuit operation. The fundamental rule is to provide the shortest path possible to make it simple for the current to return.

Designers must pay close attention to each device's high frequency filtering suggestions. More importantly, this checklist will act as a manual for generic decoupling methods and how to use them correctly:

Low inductance ceramic capacitors are used to reduce high frequency noise, while electrolytic capacitors are utilized to lessen low frequency noise on the power supply by acting as charge reservoirs for transient currents. Additionally, ferrite beads are optional but enhance isolation and decoupling from high frequency noise.

Decoupling capacitors need to be positioned as close as possible to the device's power supply pins. To reduce extra series inductance, these capacitors should be linked to greater portions of the low impedance ground plane using vias or short wires.

The device's power supply pins should be as close to the device as possible. Smaller capacitors (usually 0.01F to 0.1F) should be used. This configuration avoids the device from operating in an unstable manner when several outputs are switching at once. The distance between electrolytic capacitors and the device's power pins should not exceed one inch (10F to 100F on average).

The decoupling capacitors can be T-connected to the ground plane using vias close to the device's GND pin to simplify construction instead of constructing traces. See Figure 2 for a demonstration.

Figure 2. Decoupling Techniques for Power Pins

Ⅴ. Circuit board layer

We can examine a different part of the board design, also known as the board layer, once the component arrangement and floor plan are finished. Before PCB routing, it is highly advised to take into account the board layers, since these will influence the permissible return paths for the system design.

The vertical arrangement of copper layers of a circuit board is referred to as the "circuit board layers." These layers are responsible for controlling the board's current and signals.