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PIN Diode Application Selection Guide
SMT Attenuator Diodes

  • HSMP-381x: very low distortion attenuator
  • HSMP-383x: general purpose, low current attenuator
  • HSMP-386x: low cost, low current attenuator


1. Attenuator ICs
2. Variable Gain Amplifiers


Want pure resistance over entire bias range (bulk diode)
Useful for power set, AGC functions
Use multiple diodes in Pi, 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


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):

A measure of the amount of distortion added to a signal by a switch.

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 --------|

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 pi tau)
  where tau is the carrier lifetime.

a lower cutoff frequency means a wider range over which the diode will behave like a variable resistor.

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this page last updated: 1 October 1999