Shensi Ling implements ultra-high temperature remote temperature measurement calibration solution to effectively expand the temperature measurement range

In the field of electronic technology, there are many occasions where temperature monitoring is required to achieve the purpose of temperature monitoring, over-temperature alarm and adaptive adjustment. For example, monitoring the temperature of chips such as central processing unit (CPU), graphics processing unit (GPU) and FPGA. When the temperature of a chip exceeds the limit, the temperature can be reduced by starting the fan, reducing the operating frequency, etc., to prevent system damage and risks caused by excessive temperature.

In common remote temperature measurement solutions, discrete bipolar transistors such as 2N3904 NPN and 2N3906 PNP are used to measure remote temperature. Parasitic bipolar transistors integrated in processors such as CPUs and GPUs can also be used. After testing, it was found that when discrete transistors are used as remote temperature sensing elements, when the temperature is higher than 150°C, the temperature measurement error increases sharply due to the variation of semiconductor physical properties, making the measurement invalid.

The temperature range used by temperature measurement chips is usually (-40℃ to 125℃). When higher temperatures need to be measured, platinum resistors, thermocouples and other temperature measurement solutions are required. The working range of platinum resistors is (-200℃ to 850℃). However, since platinum resistor elements are expensive and their output is an analog voltage, additional ADC conversion is required to obtain the temperature value, so it is inconvenient to use and the cost is high. The working range of thermocouples is (-250℃ to 1800℃), but they require cold end compensation, which increases the complexity of the system.

To this end, Shensiling applied for an invention patent entitled "Ultra-high temperature remote temperature measurement calibration method, measurement calibration circuit and medium" (application number: 201911149359.4) on November 21, 2019. The applicant is Shanghai Shensiling Microelectronics Technology Co., Ltd.

Based on the relevant information currently disclosed by the patent, let us take a look at this technical solution.

As shown in the figure above, the temperature measurement circuit using discrete transistors invented in the patent includes a temperature measurement chip 140, a chip under test 150 and a discrete transistor 130. In order to accurately monitor the chip temperature of the chip under test, the discrete transistor must be placed as close to the chip under test as possible. The discrete transistor is a 2N3904 or 2N3906. By short-circuiting its collector and base, it can be equivalent to a diode, and its base-emitter voltage VBE has a certain logarithmic relationship with the bias current.

The discrete transistor is electrically connected to the temperature measuring chip, which is mainly composed of a high-temperature calibration module 280. The high-temperature calibration module can use a segmented nonlinear calibration method to set N temperature nodes T1, T2...TN in turn according to the temperature. Different calibration schemes are used in each temperature range, and error correction is performed according to different correction formulas.

In addition, the device also includes a second-order ADC module 180, which includes a modulator 181, a digital filter 182, and a digital extractor 183. The modulator, the digital filter, and the digital extractor are arranged in sequence along the signal transmission direction. The data generated by the second-order ADC module is compensated by the high-temperature calibration module 280 to generate the final temperature data, and the user can read the decimal temperature value through a universal digital bus such as I2C/SMBus.

Using the above device, the invention also provides an ultra-high temperature remote temperature measurement calibration method, using a discrete transistor with a collector and a base short-circuited, including a measurement step and an output conversion step. When performing temperature measurement, the discrete transistor is set on the chip under test, and two different current values ​​are used to excite the discrete transistor. The first transistor bias current I1 and the second transistor bias current I1 under the first current excitation and the second current excitation are recorded respectively, and the ratio of the second transistor bias current to the first transistor bias current I1 is recorded as M.

Discrete transistors are used as temperature sensing elements. When the temperature of the chip under test changes, the base-emitter electrodes of the discrete transistors will change. The temperature of the chip under test can be monitored by detecting the base-emitter voltage through the temperature measuring chip.

As shown above, the remote temperature measurement results before (left) and after (right) the high temperature calibration module is used are compared. When the temperature is higher than 160°C, there is a large measurement error due to the change in the semiconductor characteristics of the discrete transistor; after the high temperature calibration module, the remote temperature measurement linearity is greatly improved in the range of 160°C-190°C.

In addition to the intuitive temperature measurement results, the solution also shows the measured error curve. As shown in the figure above, it is a comparison image of the original error results of the remote temperature measurement before (left) and after (right) using the high-temperature calibration module. When the temperature is higher than 160°C, due to the change in the semiconductor characteristics of the discrete transistor, before high-temperature calibration, the error (160°C to 190°C) is (+1°C to -16°C). After high-temperature calibration, the error (160°C to 190°C) is (-0.5°C to 2°C), so it can meet most temperature measurement applications.

The above is the ultra-high temperature remote temperature measurement calibration solution invented by Shen Siling. Compared with the traditional remote temperature measurement solution, the biggest advantage of this solution is that it expands the temperature measurement range. It does not need to use expensive platinum resistors and complex thermocouples. It can measure temperatures up to 190°C using only a single CMOS chip and discrete transistors. It can not only reduce system costs, but also expand the application scope of this technical solution.