A Current Injection Built-In Test Technique for RF Low-Noise Amplifiers

In this paper, a practical current injection based built-in test (BIT) technique for impedance-matched RF low-noise amplifiers (LNAs) is proposed. A current generation circuit injects the RF test current at the gate of the LNA; this approach has the advantage that the matching network is not affected by the test circuitry. The technique can be used without design changes to measure the voltage gain during on-wafer test and to measure S₂₁ during final test in the presence of gate inductance and package parasitics. Furthermore, the current injection testing technique enables accurate gain measurements in order to detect faulty impedance matching networks. The proposed current-based BIT requires an on-chip voltage source, two on-chip power detectors (PDs), and an accurate external resistor. On-chip or external equipment resources are only required to measure the dc output of the PDs. As a proof of concept, a 2.1-GHz inductor-degenerated common-source LNA with a gain of 23.9 dB was designed in 0.13-mum CMOS technology together with the BIT circuitry (14% area overhead). The gain predicted by the current injection RF BIT agrees with the simulated gain using corner models within 0.8-dB error.