PIN Diode Application Selection Guide|
SMT RF Limiting Diodes
- HSMP-4820 : plastic packaged SMT limiter diode
- HSMP-3820 : higher parasitic packaged version
Integrated Circuit Amplifiers as Limiters
Self biasing PIN placed across transmission line will appear as shunt C at small drive levels, reflect at large signal levels
- Switching speed (reverse recovery time):
- HSMP-4820 : 7 nsec
- HSMP-3820 : 7 nsec
- Power handling capability:
- HSMP-4820 : 1 W CW, 100 W+ if <1msec pulse
- HSMP-3820 : 1 W CW, 100 W+ if <1msec pulse
- Needs to be near +10 dBm. If less, turns off desired signal. If more, may not protect adequately.
- Rs < 0.5
- Note: low capacitance not essential as it can be compensated for with matching
RF ID Tags (protection circuitry)
ISM (Industrial-Scientific-Medical unlicensed band use)
Anything mobile that comes within range of large interfering signals
Switching Diode Terms
Switching Speed (also called reverse recovery time)
- Reverse recovery time measures the time to switch the diode from ON to OFF. It depends on both the forward and reverse bias applied. With forward bias current, charge is stored in the I layer of the PIN diode. When a reverse pulse is applied, reverse current will flow for a brief period of time, known as the delay time, td. When a sufficient number of carriers have been removed, current begins to decrease. The time required for the reverse current to decrease form 90% to 10% is called the transition time, TT. The sum, td + TT, is the reverse recovery time.
- low reverse recovery time is better.
Power Handling Capability
- The RF power (Continuous Wave or pulsed) that can be handled safely by a diode switch. This number is limited by two factors: breakdown voltage and thermal resistance. Other factors that may influence power handling capability include ambient temperature, frequency, attenuation level, and pulse characteristics.
- high power handling capability is better.
- below threshold, a diode does not turn on (shunt C mode). Above threshold, a diode conducts (reflection mode).
Series Resistance of a PIN Diode (Rs)
- At RF frequencies a PIN diode with forward bias behaves essentially as a pure resistor, called Rs. The value of Rs is related to the bias current, the geometry of the I layer, and the properties of the carriers.
- lower is better
- Low resistance gives low insertion loss for a series switch.
- Low resistance also gives better isolation in a shunt switch.
- Low resistance is needed for best reflection, hence best isolation, in limiter (ideal is 0 )