DATA SHEET • CLA SERIES DIODES
1.00
0.75
0.50
0.25
–50
0
+50
+100
+150
Case Temperature (°C)
Figure 5. Power Handling Capability vs Temperature
During the rise time of the incident pulse, the diodes behave in
the following manner. The CLA4603, due to its thin I region, is the
first to change to a low impedance. Experiments indicate that the
CLA4603 reaches the 10 dB isolation point in about 1 ns and
20 dB in 1.5 ns with an incident power of 10 W.
Technical Description
The CLA4603 and CLA4606 limiter diodes are constructed in a
passivated flat-chip configuration and are available in a basic chip
form or encapsulated in several Skyworks hermetic ceramic
packages.
The CLA4606 takes about 4 ns and the CLA4607 about 50 ns to
achieve 10 dB isolation. Consequently, the CLA4603 provides
protection during the initial stages of pulse rise time with the
thicker diodes progressively “turning on” as the power increases.
With proper spacing (X1 and X2), the “on” diodes reflect high
impedances to the upstream diodes, reducing the turn-on time for
those diodes and ensuring that essentially all of the incident
power is reflected by the input diode, preventing burnout of the
thinner diodes.
Limiter diodes with lower capacitance values to 0.08 pF and
constructed with a passivated mesa configuration are available in
the CLA4601 and CLA4605 series. The mesa devices offer low
capacitance and, therefore, broader bandwidth, lower loss, and
faster response at reduced power. These diodes are also available
in chip package form and represent the ultimate in limiter
performance not approached by other manufacturers.
The CLA4607 diodes (highest power) are available in both planar
and mesa construction.
At the end of the pulse the process reverses and the diodes
“recover” to their high impedance states; the free charge that
was injected into their I regions by the high-incident power signal
leaks off through the ground return and is also reduced by internal
recombination. With a ground return, recovery time is on the order
of 50 ns. With a high impedance return (for example, the circuit
shown in Figure 10), the Schottky diode (such as the CDF7621-000)
recovers or “opens” in practically zero time. Internal recombination
on the order of several diode lifetimes is the only available
Figures 6 and 7 illustrate the fundamental structures of diodes
mounted in a 50 Ω microstrip circuit.
Additional bonding and handling methods are contained in the
Skyworks Application Notes, Waffle Pack Chip Carrier
Handling/Opening Procedure (document #200146) and Diode
Chips, Beam-Lead Diodes, Capacitors: Bonding Methods and
Packaging (document #200146).
mechanism for recovery of the limiter diodes. This recovery time
can be long – on the order of 1 ms for the CLA4607 series. The
shunt resistor (RR) minimizes the problem. One hundred Ohms
approximately doubles the recovery time compared to a short circuit.
Basic Applications
In microstrip limiters, the bonding wire length and diameter
together with the chip capacitance, form a low-pass filter (see
Figure 8). Line lengths (X1 and X2) are varied to provide
broadband matching and flat leakage characteristics. Typically,
X1 and X2 are on the order of 0.1 wavelength. In Figure 9, the
CLA4607 chip provides about 20 dB attenuation, reducing a 1 kW
input signal to a 10 W output signal. The CLA4606 reduces this to
100 mW and the CLA4603 to about 20 mW.
When the Schottky diode is directly coupled to the transmission
line in cascade after the coarse limiter, the leakage power is less
than if a 0 Ω ground return were used. If the Schottky is
decoupled too much, the leakage power increases due to the high
DC impedance of a Schottky. Similarly, a 3 Ω ground return
causes an increase of about 3 dB in leakage power compared to a
0 Ω return.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
200100I • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • September 28, 2009
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