L
Admin
[Technical article / FAQ, rfforum Editorial Team]
Front-end protection is drawn as a harmless block before the LNA. On the bench, PIN limiters, TVS diodes, and gas tubes add loss, capacitance, and sometimes slow recovery that looks like "LNA memory" after a strong pulse.
1. What protection actually costs
- Insertion loss before the LNA adds almost 1:1 to system NF; a 0.5–1 dB protector is a noise budget line, not a footnote
- Capacitance and package parasitics pull match and can create out-of-band resonances that look like blocker susceptibility
- After a strong pulse, some limiters take microseconds to milliseconds to recover; a swept NF or ACLR test can catch the device mid-recovery
2. Freeze list before you blame the LNA die
- Protector PN, measured IL, and whether it sits before or after the first match network
- Recovery-time note next to any pulsed NF, desense, or "sticky" gain claim
- ESD / surge test level that justified the protector, so you can revisit if the RF cost is no longer worth it
- Whether cal / fixture includes the protector (removing it for "better NF" is a different product)
3. Habit
Archive protector IL and recovery next to every front-end NF number. If two board spins differ only in the limiter diode, treat that as an NF and match change.
Discussion: on your last front-end NF miss, did the fix land in protector IL, match, or the LNA itself — and do you require a recovery-time check after pulse desense tests?
— rfforum 编辑部 / Editorial Team
Front-end protection is drawn as a harmless block before the LNA. On the bench, PIN limiters, TVS diodes, and gas tubes add loss, capacitance, and sometimes slow recovery that looks like "LNA memory" after a strong pulse.
1. What protection actually costs
- Insertion loss before the LNA adds almost 1:1 to system NF; a 0.5–1 dB protector is a noise budget line, not a footnote
- Capacitance and package parasitics pull match and can create out-of-band resonances that look like blocker susceptibility
- After a strong pulse, some limiters take microseconds to milliseconds to recover; a swept NF or ACLR test can catch the device mid-recovery
2. Freeze list before you blame the LNA die
- Protector PN, measured IL, and whether it sits before or after the first match network
- Recovery-time note next to any pulsed NF, desense, or "sticky" gain claim
- ESD / surge test level that justified the protector, so you can revisit if the RF cost is no longer worth it
- Whether cal / fixture includes the protector (removing it for "better NF" is a different product)
3. Habit
Archive protector IL and recovery next to every front-end NF number. If two board spins differ only in the limiter diode, treat that as an NF and match change.
Discussion: on your last front-end NF miss, did the fix land in protector IL, match, or the LNA itself — and do you require a recovery-time check after pulse desense tests?
— rfforum 编辑部 / Editorial Team
