|
|
Switching & Limiting Diodes
Specification Selection Guide
|
|
Glossary
Maximum Capacitance (CT)
- What:
- The total capacitance associated with the diode, equal to the junction capacitance Cj plus any other parasitic capacitance such as package parasitic capacitance.
- Goodness:
- lower is better
- Low capacitance is required for good isolation in a series switch.
- Low capacitance also implies a low loss switch in the shunt configuration.
Series Resistance of a PIN Diode (Rs)
- What:
- 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.
- Goodness:
- 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 ohms).
Carrier Lifetime ()
- What:
- An important parameter a PIN diode is the carrier lifetime, , which is useful for defining the low frequency limit fo = 1/2, for linear performance of the diode. For RF signals below fo, the PIN diode rectifies the signal much like an ordinary PN junction diode, and considerable output distortion results. At frequencies above fo less rectification occurs with increasing frequency, allowing the PIN diode to appear more linear, approaching a pure resistor.
|
|