Improving Receiver Sensitivity

Improving Receiver SensiTIvity with External LNA

Abstract: This applicaTIon note presents the system level trade-offs involved in adding a low-noise amplifier (LNA) to a remote keyless entry (RKE) receiver. The system's sensiTIvity improves 3.77dB, but the third order intercept degrades by 15dB.

The sensiTIvity specifications indicates how well a receiver will capture weak signals. It is a key specification becauseand it directly affects the range of the system.

In many remote keyless entry (RKE) and tire pressure monitoring (TPM) designs, the manufacturer will quote the sensitivity of the receiver (dBm) as a means to differentiate the system from a competitor's. Other receiver parameters such as noise figure, intermodulation distortion, dynamic range or even power consumption are sometimes relegated in importance because of the importance that consumers place on sensitivity and range.

One way to improve a system's sensitivity is to add gain by connecting an external LNA. Or -- is it that simple?

Sensitivity of a receiver is based on its noise figure, the minimum required S/N ratio for detection of the modulation, and the thermal noise of the system. The equation for the minimum input signal is noted below:

S = NF + n0 + S/N