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PIN Diode Application Selection Guide
SMT Attenuator Diodes
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- HSMP-381x: very low distortion attenuator
- HSMP-383x: general purpose, low current attenuator
- HSMP-386x: low cost, low current attenuator
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Alternatives:
1. Attenuator ICs
2. Variable Gain Amplifiers
Features:
Want pure resistance over entire bias range (bulk diode)
Useful for power set, AGC functions
Use multiple diodes in  , T, or bridged T configuration for constant impedance throughout the attenuation range,
Key Parameters:
- Intercept point (IP2):
- 60 -120 dBm
- HSMP-381x: extremely low distortion @ low R: 120 dBm
- Cutoff frequency (fc):
- 5 kHz to 16 kHz for Bulk diodes; 3 MHz to 32 MHz for epi diodes
- HSMP-381x: fc = 106 kHz
- HSMP-383x: fc = unspecified
Markets:
TV satellite receivers (DBS, TVRO)
Cellular, PCS
ISM (Industrial-Scientific-Medical unlicensed band use)
Attenuator Diode Terms
Second Order Intercept Point (IP2)
(also known as 2nd Harmonic intercept point):
- What:
- A measure of the amount of distortion added to a signal by a switch.
- Goodness:
- higher IP2 is better.
Cutoff frequency (fc)
Diode acts like a
pn junction device |
Diode acts like a
current-controlled inductor or capacitor |
Diode acts like a
current-controlled resistor |
| |------ <0.1 fc ------| |
---- 0.1 < f/fc <10 ---- |
|------- >10 fc --------| |
- What:
- An indicator of the frequency range over which a PIN diode acts as a variable resistor, a necessary characteristic for proper operation as an
attenuator. The frequency of operation (f) of a diode intended to be used as a current-variable resistor should be at least 10 times higher than the cutoff frequency. The value of fc can be calculated from:
fc = 1 / (2  )
- where is the carrier lifetime.
- Goodness:
- a lower cutoff frequency means a wider range over which the diode will behave like a variable resistor.
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