Low power consumption analysis instrument verifies 2G mobile communication current peak value

ben_0101

Low power consumption analysis instrument verifies 2G mobile communication current peak value [Copy link]

Recently, I developed a device based on 2G communication, but it is not used in China. It seems that the 2G service in China is gradually withdrawing from the network. Currently, only China Mobile supports 2G service. I use Quectel's MC25 module for Open development, mainly to save costs. The current stable MCU is too expensive, and I dare not use domestic MCUs because there are too many pitfalls.

During the test, it was found that the battery voltage would drop whenever data communication was performed. I also saw such description in the MC25 specification (as shown in the figure below). When GSM transmits data, it will generate a current pulse of about 4.6ms, and this pulse is also the root cause of the voltage drop.

I asked many friends in the communications field, and they all said that 2G does have such a phenomenon, but they have not observed it in detail. In order to understand the phenomenon of current pulse and voltage drop, I used the DC power analyzer mPower1203 to verify the current waveform.

First, I used the mPower1203 instrument to directly power the device, obtained the waveform reported by the data, and saved it for later analysis.

Zooming in on the waveform, we can see that there are many periodic pulses during the data communication period, and measuring the pulse period, it is indeed around 4.6ms. It turns out that the voltage drop is indeed caused by these large current pulses.

Continue to measure the pulse width, which is about 578us, which is basically consistent with the pulse time of 577us in MC25.

With these real test data, we can indeed intuitively determine the source of the voltage drop, which can provide a great reference for evaluating the capacitance added to the VBAT of the module.

According to the MC25 specification, if the RF signal environment is not good and the MC25 uses the maximum transmit power for communication, the peak current of 577us may reach 1.6A. If the maximum voltage drop is 400mV, and if only capacitors are used to provide pulse current, the theoretical capacitance can be calculated as:

However, in fact, the capacitor only bears part of the current function, and the rest is provided by the battery, which depends on the on-resistance value of the battery protection board. If the resistance value is particularly small, the capacitance used will be relatively small, but 100uF capacitance is generally recommended. However, if the on-resistance value is relatively large, such as more than 100mR, it is recommended to keep more capacitance at VBAT of MC25. Our 2G communication device has added 470uF capacitance, just in case, of course, it would be even better to use low ESR tantalum capacitors.

秦天qintian0303

Does China Telecom also not support 2G? China Unicom definitely does not support 2G

qwqwqw2088

Mobile still has 2G network