Lug Terminal,Spade Terminal Connectors,Ring Terminal Connector,Spade Wire Connectors Wonke Electric CO.,Ltd. , https://www.wkdq-electric.com
Since the introduction of integrated circuits, temperature sensors have become an essential part of IC design. Engineers have long sought to minimize the impact of temperature on chip performance. Integrated temperature sensors are capable of addressing most temperature sensing challenges within a wide range of -55°C to 200°C. The latest generation of these sensors can achieve an impressive accuracy of ±0.4°C in a compact 0.76mm² package.
From the early days of IC development, temperature sensors have naturally become embedded in device designs. While many designers focused on reducing temperature-related effects, some began exploring alternative approaches. One innovative idea was to leverage the temperature-dependent behavior of the pn junctions in active circuits rather than trying to suppress them. This shift in thinking opened up new possibilities for integrating digital functions and improving sensor performance.
The internal operation of an integrated temperature sensor relies on the ambient temperature affecting the behavior of transistors inside the package (see Figure 1). By carefully configuring and calculating the transistor characteristics, the sensor can eliminate the influence of saturation current (IS). This is typically done using a constant current source and switching between different transistor configurations.
In Figure 1, we see how the difference between VBE and VBE(N) corresponds to temperature changes. The base-emitter voltage (VBE) of a single transistor is given by:
$$
V_{BE} = \frac{kT}{q} \ln\left(\frac{I_C}{I_S}\right)
$$
Where:
- $ k $ is the Boltzmann constant ($1.38 \times 10^{-23}$ J/K),
- $ q $ is the elementary charge ($1.602 \times 10^{-19}$ C),
- $ T $ is the absolute temperature in Kelvin.
For multiple parallel transistors, the base-emitter voltage becomes:
$$
V_{BE(N)} = \frac{kT}{q} \ln\left(\frac{I_C}{N I_S}\right)
$$
When the current source is switched between two transistors, the difference in their base-emitter voltages is:
$$
\Delta V_{BE} = \frac{kT}{q} \ln(N)
$$
This value, often represented as a constant equal to $ 86.25 \times 10^{-6} \times \ln(N) $, allows for accurate temperature measurement at the IC level. With further circuit improvements, modern temperature sensors can achieve high precision, such as ±0.4°C.
Once the temperature is measured, it must be output to the external world. There are two main methods: analog voltage or digital signals. Analog outputs are straightforward and easy to interpret, while digital outputs offer more flexibility and can be transmitted via various interfaces.
Digital temperature sensors typically use protocols like 1-wire, 2-wire (I2C/SMBus), or 3-wire (SPI). These allow for precise control and communication with other system components. For example, 1-wire outputs can provide PWM or threshold-based signals useful in fan control systems, while SPI interfaces enable high-speed data transfer.
Another significant advancement in temperature sensor technology is wafer-level packaging (WLP). This technique, developed in the late 1990s by Sandia National Laboratories and Fujitsu, allows for ultra-compact packages that are assembled using standard SMT processes. WLP reduces the thermal resistance between the junction and the environment, making it ideal for high-performance applications.
The latest WLP temperature sensors are incredibly small—smaller than a typical 0.1μF capacitor in a 0603 package (see Figure 2). This miniaturization enables placement of the sensor almost anywhere on a PCB, much like sprinkling salt and pepper on a plate.
With a footprint of just 0.76mm², the latest temperature sensors deliver ±0.4°C accuracy while occupying minimal space. This makes them ideal for a wide range of applications, from consumer electronics to industrial systems. As the demand for smaller, more efficient devices continues to grow, temperature sensors will play an increasingly vital role in ensuring reliable performance across all environments.