Receiver Sensitivity

Receiver sensitivity is the minimum signal level at a receiver input that still meets a stated performance target. The target might be packet error rate, bit error rate, demodulation margin, image detectability, radar detection probability, optical link acceptance or a weak-signal measurement repeatability limit. A sensitivity number without the target condition is not an engineering specification.

Sensitivity is usually expressed in dBm for RF or optical links, but the same idea appears in volts, watts, counts, optical power or calibrated engineering units. The value depends on receiver bandwidth, noise figure, waveform, coding, detector, target error rate, implementation loss and measurement boundary.

Basic Receiver Screen

A common RF screening relation is:

where:

• N_{dBm} is receiver noise floor at the stated bandwidth;
• SNR_{req} is the required signal-to-noise ratio for the waveform and target error rate;
• L_{impl} is implementation loss or detector penalty.

If a design margin is required, the received signal should satisfy:

and the required acceptance condition may be:

The margin requirement is not part of the receiver sensitivity itself; it is a project decision layered on top of sensitivity.

Noise Floor Connection

At room temperature, an RF receiver noise floor can be estimated as:

where B is bandwidth in hertz and NF is system noise figure in dB. Wider bandwidth increases noise floor, so sensitivity becomes less negative unless the required SNR or receiver architecture changes.

This is why receiver sensitivity cannot be compared across data sheets unless bandwidth, waveform, coding, target error rate and test method match.

Worked RF Example

A wireless receiver has:

• bandwidth B=200000 Hz;
• system noise figure NF=5 dB;
• required SNR 12 dB;
• implementation loss 2 dB.

The noise floor is:

The receiver sensitivity is:

If the measured received signal is:

then the operating margin over sensitivity is:

If the design requires 6 dB margin, the link passes this sensitivity screen.

Now increase bandwidth to 1 MHz with all other values unchanged. The noise floor rises by:

The sensitivity becomes:

The same -91 dBm received signal now has only 4 dB margin, so it fails a 6 dB design-margin requirement even though the receiver hardware did not change.

Optical Links

In optical fiber systems, receiver sensitivity is usually specified at a bit rate, modulation format, wavelength, extinction ratio, target BER and receiver type. A first-pass margin is:

The received power must also remain below receiver overload. A fiber link can exceed receiver sensitivity and still fail because of dispersion, reflection, dirty connectors, modal effects, jitter, extinction-ratio penalty or overload.

Difference From Noise Floor And Dynamic Range

Noise floor is a noise level. Receiver sensitivity is a required signal level that adds required SNR or detector criteria to the noise floor. Dynamic range compares the lower useful signal boundary with the upper overload or compression boundary. A receiver can be sensitive in a quiet lab and still fail in the field because it has poor blocking, intermodulation, adjacent-channel rejection or overload recovery.

Validation Evidence

A defensible sensitivity statement includes receiver input reference plane, bandwidth, noise figure, waveform, modulation and coding, data rate, target error rate, temperature, antenna or optical interface assumptions, filtering, detector mode, implementation loss, calibration state and test method. Field validation should also record interference, occupancy, packet error, EVM, received signal strength, noise floor, overload indicators and margin over the required threshold.

Common Mistakes

Common mistakes include treating receiver sensitivity as a range guarantee, comparing sensitivity values measured at different bandwidths, ignoring coding rate and target BER, using clear-channel sensitivity when interference dominates, adding design margin twice, forgetting implementation loss, ignoring optical receiver overload, and improving sensitivity when the real failure is strong-signal desensitization.

The practical rule is to state the minimum signal, the exact condition under which it applies and the margin required for the service decision.