What is the difference between sensitivity and selectivity in a receiver?
Sensitivity and Selectivity Compared
Sensitivity and selectivity are the two most fundamental specifications of any receiver. Sensitivity determines whether a weak desired signal can be detected at all. Selectivity determines whether a desired signal can be received in the presence of nearby interferers.
| Parameter | Superheterodyne | Direct Conversion | Digital IF |
|---|---|---|---|
| Image Rejection | 60-90 dB (filter) | 30-50 dB (mismatch) | N/A (digital) |
| DC Offset | No issue | Major issue | No issue |
| LO Leakage | Low | High | Low |
| Integration | Difficult | Easy (single chip) | Moderate |
| Dynamic Range | 80-120 dB | 60-90 dB | 70-100 dB |
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
- Interface compatibility: verify impedance, connector type, and mechanical form factor match the system architecture
- Margin allocation: include sufficient design margin to account for manufacturing tolerances and aging effects
Frequently Asked Questions
Can I improve sensitivity without affecting selectivity?
Yes. Reducing the noise figure (better LNA) improves sensitivity without changing selectivity. The filter characteristics remain the same; only the noise floor changes.
Can I improve selectivity without affecting sensitivity?
Partially. A better filter (steeper skirts, same passband bandwidth) improves selectivity. However, any filter adds insertion loss, which degrades sensitivity unless compensated by additional gain.
Which matters more in dense environments?
Selectivity often matters more because strong adjacent-channel signals can desensitize the receiver through intermodulation and blocking. In these environments, the practical sensitivity is limited by interference, not thermal noise.