Meaning
Interference in high-frequency receivers can arise when strong out-of-band signals drive the input amplifier beyond its linear range. In these situations, lna rectification occurs as the nonlinear transfer function of the low noise amplifier acts like a diode detector, converting the envelope of the interfering signal into a spurious direct-current or low-frequency bias offset. This induced offset alters the operating point of subsequent stages in the receiver.
Nonlinear Mechanism
Active semiconductor channels exhibit non-ideal current-voltage characteristics that become pronounced under large-signal excitation. When a strong blocker signal is present, the second-order nonlinearity of the amplifier produces a rectification product. This lna rectification generates a slow-varying voltage that mimics a change in bias.
The shifts in the internal operating points decrease the gain of the amplifier and can lead to severe intermodulation distortion.
Receiver Degradation
Direct-conversion receivers are exceptionally vulnerable to low-frequency offset voltages appearing at the mixer inputs. Because the spurious voltage produced by lna rectification falls directly into the baseband frequency range, it can saturate the analog-to-digital converter. This saturation renders the receiver deaf to the weak desired signal.
Consequently, the signal-to-noise ratio drops, which leads to high packet error rates in wireless communication links.
System Mitigation
Alleviating the effects of unwanted signal conversion requires front-end filtering. An input bandpass filter can attenuate strong out-of-band signals before they reach the amplifier. Designers also select amplifiers with a high second-order intercept point to ensure linear operation even in the presence of strong nearby transmitters.
