In circuit design, there are often principles that engineers assume to be correct, but in reality, they may lead to issues in performance or efficiency. Here are eight common circuit design misunderstandings every electronics engineer should be aware of:

Misunderstanding 1: Thin Wires and Automatic Routing Are Good Enough for Low-Requirement PCB Design

Comment: While automatic routing might seem convenient, it increases the PCB area and the number of vias significantly, impacting manufacturing costs and yields. PCB manufacturers consider factors such as line width and via count when determining pricing. Manual routing is often more efficient, improving the PCB yield and reducing the cost by saving drill bits and space.

Misunderstanding 2: Pull-Up Resistors on Bus Signals Ensure Signal Stability

Comment: Although pull-up and pull-down resistors are often necessary, not every signal needs one. When a signal is driven, the current can reach milliampere levels, leading to increased power consumption. In complex systems with 32-bit address/data buses and other signals, excessive pull-ups can consume several watts. Proper design analysis can help determine where resistors are needed.

Misunderstanding 3: Leaving Unused I/O Ports Floating Is Harmless

Comment: Floating I/O ports, especially in CPUs and FPGAs, can oscillate due to external interference, increasing power consumption. To avoid this, unused I/O pins should be set as outputs. Leaving them floating may lead to unnecessary power draw due to repeated toggling.

Misunderstanding 4: Maximizing FPGA Gates Utilization Is Always Beneficial

Comment: While an FPGA may have many available gates, using all of them can significantly increase power consumption. The number of flip-flops and triggers in use determines the power draw, and it’s possible for the same FPGA to consume vastly different amounts of power depending on the design. Optimizing the number of high-speed flip-flops is crucial for minimizing power usage.

Misunderstanding 5: Small Chips Have Insignificant Power Consumption

Comment: The power consumption of small chips, such as ABT16244, is primarily determined by the current at the pins. Even though they may have low no-load power consumption, under full load, each pin can drive significant current (e.g., 60 mA), resulting in much higher overall power consumption than initially expected.

Misunderstanding 6: Grounding the Chip Select (CS) Pin Will Speed Up Memory Read Operations

Comment: Grounding the chip select (CS) pin to speed up memory access can lead to excessive power consumption. When the CS is active, memory power consumption can increase dramatically compared to when it’s inactive. Therefore, it’s essential to control the CS pin properly and keep the chip select pulse as short as possible while ensuring reliable operation.

Misunderstanding 7: Overshoot in Signals Can Always Be Eliminated by Matching

Comment: Overshoot is common in most signals, and trying to match them perfectly is often unnecessary. Signals like TTL or LVDS don’t need precise matching, and attempting to do so could result in excessive power consumption or signal amplitude reduction. Instead, focus on ensuring that the overshoot is within acceptable limits, especially when dealing with signals with varying output impedances.

Misunderstanding 8: Power Consumption Optimization Is Solely the Responsibility of Hardware Engineers

Comment: Power consumption isn’t just a hardware issue—software plays a crucial role. Software controls signal flips and memory accesses, and optimizing these can significantly reduce power consumption. Reducing external memory access, using cache efficiently, and responding to interrupts promptly are all software strategies that can help minimize power consumption.

Conclusion:

Understanding these common misunderstandings in circuit design is essential for engineers who want to improve efficiency, reduce power consumption, and design more reliable systems. By addressing these myths, you can avoid co