Due to the problem of radio interference of GSM mobile phones, GSM mobile phones operate in TDMA mode, and radio frequency transmission and reception cannot be performed at the same time. The basic principle of RF mobile phone interference reduction is to strengthen matching and isolation.
In the design, please consider that the transmitter is in high power transmission state, which is more likely to cause interference than the receiver, so it is necessary to ensure the matching of the power amplifier (PA) . In addition, the isolation of the RF front filter is also an important indicator. The PCB is usually 6 or 8 layers, and there should be enough ground plane to reduce RF interference.
Some simpler devices can only block a set of frequencies, while advanced cell phone jammer can block multiple types of networks at the same time, cutting off the signal of dual-mode or triple-mode phones, making it impossible to switch between different networks. and find an opening signal. Some high-end jammers can block all frequencies at the same time, while other gsm jammers can be set to block specific frequencies.
It is especially emphasized that the radio frequency system will cause electromagnetic interference on the digital baseband (DBB) and analog baseband (ABB). Strengthening the radio frequency shielding is an effective measure. He also pointed out that the TDMA noise and burst noise generated in the communication between the mobile phone and the base station will bring more obvious noise to the baseband speech processing and should be carefully suppressed. In addition, TDMA noise mainly affects the voice part of the cellphone, so please pay attention to the PCB layout and the wiring of the voice part.
Some engineers have pointed out that PA matched filtering has the ability to suppress spurious radiation, but there are still limitations. Are there other solutions? You can choose a good front filter to improve out-of-band rejection. When it comes to resolving RF power interference and choosing RF LDO, you must first make sure that the RF power has been properly filtered. Second, if necessary, it is better to use separate power supplies for different RF circuits. When choosing an RF LDO, please pay attention to its characteristics, such as drive current, output noise, and ripple suppression.