The tolerance of RF ICs against on-chip in-band interferers is diagnosed from the viewpoints of the quality of wireless channels compliant with LTE standards. The on-chip interferers inevitably propagate from other active circuits like digital backend processors through silicon substrate coupling in the same die of system-level integration. An in-system diagnosis platform of RF ICs presented in this paper relates the impacts of such interferers on the circuit-level response and system-level communication performance metrics. The figures of communication quality at a system level, like EVM, BER and throughput are concurrently evaluated with the strengths of interferers in different forms and at different locations in a silicon chip. The interferers are measured as the in-band signal to spurious power ratio at the output of RF ICs, the magnitude of substrate voltage fluctuations at the proximity of RF ICs, and related with the amount of power current consumed by base-band digital ICs. The tolerance of RF ICs is represented by the maximum strength of on-chip interferers for sustaining prescribed communication performance. The diagnosis system is divided into two parts, (i) a system-level RF simulator handling modulation and demodulation of real communication vectors in LTE format and also enabling hardware connectivity with RF ICs, and (ii) a silicon emulator of on-chip interferers coupled to the RF ICs. A 65 nm CMOS chip incorporates an on-chip arbitrary noise generator, an on-chip waveform capture, and RF IC for LTE receiver front end, and demonstrates the entire diagnosis.