Power consumption is a well-worn topic. Most people have some understanding of it. Currently, many products use low power consumption as a selling point in their marketing. To enhance everyone's understanding of power consumption, this article will introduce it from two aspects: 1. Key design methods for low power consumption, and 2. Key points of low power consumption design for microcontroller systems. If you are interested in power consumption, please continue reading.
I. Low-power design methods
1. Parallel Structure
Parallel architectures decompose the work of one data path onto two paths. The main reason parallel architectures reduce power consumption is that, while achieving the same computational speed as the reference architecture, their operating frequency can be reduced to half, and the power supply voltage can also be lowered. Parallel circuit architectures reduce power consumption by sacrificing chip area. If a parallel architecture is used, the operating frequency can be reduced to half, and the worst-case latency can reach 2. Assuming the power supply voltage is reduced to 1.8, due to the doubled circuitry and increased external wiring, the equivalent capacitance is 2.
2. Flow structure
Pipelining reduces power consumption by inserting registers to shorten combinational paths. Consider a circuit that first adds and then compares, with a pipelined register inserted in the middle. The adder and selector are on two different combinational paths. The operating frequency remains unchanged, but the number of circuit stages is reduced, allowing for a lower supply voltage. Assuming a supply voltage of 1.8V, the equivalent capacitance becomes 1.2V due to the pipelined register. Therefore, as shown in the equation, pipelining can significantly reduce power consumption.
Pipelining and parallelization of circuits can reduce power consumption because designers can choose the operating voltage of the circuit. If the operating voltage is fixed, these two methods can only increase the operating speed of the circuit, but power consumption will increase accordingly.
3. Coding optimization
One-Hot code, Gray code, and bus inversion code can generally be used to reduce the power consumption of the on-chip system bus.
One-Hot code allows only one bit in a binary number to differ from the values of the other bits; Gray code differs by only one bit in the binary code of any two consecutive numbers. Because it involves fewer transitions when accessing the contents of two adjacent addresses, it effectively reduces bus power consumption. Bus inversion code considers the relationship between adjacent data when transmitting data to determine the transmission format. When the transmitting component transmits the first piece of data onto the bus, it compares it with [previous data], and decides whether to transmit or not based on the comparison result, thereby reducing the effective number of bus inversions and thus reducing system power consumption.
II. Key Considerations for Low-Power Design of Microcontroller Systems
To meet the low-power requirements of a microcontroller system, selecting a microcontroller with low-power characteristics is a straightforward solution. Low-power microcontrollers can significantly reduce system power consumption. The low-power characteristics of a microcontroller can be assessed from several aspects, including its power supply voltage, internal structure, system clock, and low-power modes. Generally, when selecting technology suppliers and products, users need to consider the following important hardware parameters in greater depth:
1. Choose a simple CPU core
When choosing a CPU core, avoid blindly pursuing performance; adhere to the principle of "good enough." If an 8-bit machine is sufficient, there's no need to choose a 16-bit or 32-bit machine. The faster a microcontroller runs, the higher its power consumption tends to be. The more complex, highly integrated, and powerful a CPU is, the more transistors it has, and the greater its total leakage current. Even when entering a stop state, the leakage current becomes significant. In contrast, a simple CPU core not only has low power consumption but also low cost.
2. Select a microcontroller system with low-voltage power supply.
The low supply voltage of a microcontroller system effectively reduces its power consumption. Due to advancements in semiconductor manufacturing processes, the supply voltage of microcontrollers has decreased from 5V to 3.3V, 3V, 2V, and even 1.8V. This low supply voltage not only reduces the power consumption of the microcontroller itself but also reduces the power consumption of its peripheral circuits.
3. Select a microcontroller system with a low-power mode.
Low-power modes refer to system modes such as Idle, Stop, and Suspend. Power consumption in these modes is significantly lower than during normal operation. In Idle mode, the CPU stops working, but the internal system clock continues, and the microcontroller's peripheral I/O modules also continue operating; system power consumption is generally reduced only slightly, approximately 50% of the power consumption in normal operating mode.
If all analog peripherals are turned off when the CPU enters Stop mode, power consumption can be reduced to the nA level. However, in Stop mode, the CPU needs to reinitialize the system after waking up, and the contents of all special function registers will be reinitialized. This needs to be considered in some low-power applications.
In Suspend mode, the CPU and internal system clock stop working, I/O modules are suspended, data stored in on-chip RAM is preserved, and CPU power consumption can be reduced to the nA level. The system is woken up by a wake-up event. When the CPU is woken up, the system is not reset by the CPU and continues executing the program from where it entered Suspend mode. This is an ideal low-power mode.
At the hardware level, it is essential to carefully measure the parameters mentioned above. In addition, choosing a suitable clock scheme and using power consumption per MIPS to measure the low-power performance of the MCU are also crucial.
