In the design process of the GSM single-card single-standby device and the dual-card dual-standby device currently developed on the MTK platform, the phenomenon of restarting the mobile phone (re-searching the network) often occurs. Although the design capabilities of Chinese engineers in mobile phone RF have been continuously improved in recent years, some of the "big boss" problems in the specific RF design process still plague the majority of engineers. For superheterodyne frequency conversion, low noise design, PLL circuit, local oscillator circuit, signal processing, power management, etc. are actually interrelated, circuit matching and PCB layout are also a key step to solve the restart problem, these are the theoretical basis Inseparable from the accumulation of experience. Of course, the "big boss" often means that we will increase R & D costs and investment more, so we need to have some new ideas and new methods to effectively solve the restart problem in this design. First analyze the reasons for the restart of the MTK platform mobile phone: When the MTK platform mobile phone system goes from the sleep state to the wake-up state, TCXO, CLKSQ & PLL will be interrupted at this time, which will cause harmonic and noise interference of the TCXO crystal clock and the signal output by the PLL, causing the machine to restart. What I want to introduce here are two ways to solve the restart problem in the MTK platform: First, let's analyze the basic working principle of MT6129 RF IC MT6129 provides GSM900 / DCS1800 / PCS1900MHz three-band transceiver channel, including receiving circuit, transmitting circuit, frequency synthesis circuit (PLL), local oscillator circuit and TX VCO and corresponding control circuit. The pin directly outputs the signal to the BBP SYSclk part. It is precisely because of the key signal input to the BBP SYSclk that we need further analysis. The specific circuit block diagram is shown in Figure 1. Figure 1: MT6129 wireless transmission block diagram. Second, the specific application and implementation of the hardware circuit Figure 2: RF6129 specific application circuit. Figure 3: Simple functional block diagram inside MT6129. The 26MHZ clock is sent by u603 4 # output to 29 # of MT6129. There are two channels in 6129. One channel is amplified by internal operational amplifier and output from 31 # to A2 # of CPU (BB IC) as the main clock. The other channel is used as the basic pin reference The frequency is sent to the internal phase discrimination circuit. However, if there is clutter and noise interference in the 26MHZ master clock signal output from MT6129 31 # or MT6139 22 #, the signal reception of the mobile phone will be poor and the machine will restart. In order to effectively solve this problem, there are currently two solutions: Figure 4. Add a 39PF capacitor to the output line at 22 #. A higher harmonic is generated when the MT6139 22 # is output. Adding a 39P capacitor can filter this higher harmonic so that the output filtering function can be increased. The output waveform becomes smooth to reduce harmonic interference. Therefore, the restart problem can be solved in this way. The second method: Figure 5. Replace the capacitance of C209 1NF with Murata's magnetic beads BLM15HD182SNE, because the signal of 26MHZ is sent to the BB IC and there is noise figure interference. It is precisely because of this interference that the machine has restarted. Replacing the capacitor with magnetic beads (inductance) is mainly to improve the noise figure interference. In summary: the two solutions are to filter and improve the interference of higher harmonics, clutter and noise coefficient, and the difference between the two solutions is: the first method directly outputs the signal from the RF IC REFOUT pin When filtering out clutter, the second method uses magnetic beads to reduce the noise interference of the RF IC output signal and make the output signal smoother. If the actual development is still in the EVT, DVT, and PVT phases, the first method is ideal. If the machine being developed is in mass production, please use the second method. These two design solutions to solve the restart problem Has passed the actual mass production verification, it is worth promoting.
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the first method:
At present, there are many solution companies in the mainland China market that use MTK6226, MTK6225, MTK6223 and other chip solutions from Taiwan ’s MTK company for mobile phone design. And launch.