1. Field of the Invention
The present invention relates to avoidance of receiver desensitization, and more particularly, to methods for ensuring the sensitivity of an RF receiver module within an electronic device by avoiding the interference caused by other circuits of the electronic device, and the electronic devices using the same.
2. Description of the Related Art
Taking a Global System for Mobile Communications/General Packet Radio Service (GSM/GPRS) chip as an example, essential electronic components, such as digital base-band (DBB) circuits, analog base-band (ABB) circuits, a power management unit (PMU) and a radio frequency (RF) transceiver are integrated into a single chip (System on Chip, SOC). In addition, the GSM/GPRS chip may have peripheral supports such as a digital camera, a high speed Universal Serial Bus (USB) and a class D audio amplifier (AMP).
Conventionally, the RF receiver and the baseband circuits are implemented on individual chips, and the interference of the baseband circuits with the RF receiver may be reduced by using shielding room. Once the baseband circuits and the RF receiver are integrated into a SOC, however, problems of interference from the baseband circuits to the RF receiver may occur. Sometimes the interference may originate from the coupling of high frequency harmonics of the system clock, receiver (Rx) input pads, VCO (voltage-controlled oscillator) Vtune signals and so on, where a harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency: for example, if the fundamental frequency is f, the harmonics have frequencies 2f, 3f, 4f, and so on. Sometimes the interference couples into the RF receiver, and thereby causes RF de-sensitization. The noises may hit the channel (e.g., a GSM channel) and degrade the Rx performance. Assuming that the Rx sensitivity is −109 dBm and the SNR is 6 dB, the Rx noise level has to be less than −115 dBm. If the clock source is a 1V 26 MHz square-wave, its 35th harmonic (936 MHz) is −18.7 dBm. As a result, 100 dB attenuation is required to isolate the interference from coupling to the RF circuits.
Therefore, a method and a system for diminishing interference of the RF circuits of an SOC by digital parts of the SOC and for lessening the RF de-sensitization phenomenon is required.