More about diodes!

Need a pn junction diode that has a high reverse breakdown, very low capacitance ( so its fast) and low resistance in the forward direction? If this is the case then a simple pn junction diode may not provide the answer. The reason is, that as the breakdown voltage goes up, the forward resistance goes up, capacitance goes down. If you a need a lot of current then this diode will not provide it. As the resistance goes down the breakdown goes down and the capacitance goes up. So sometimes a simple pn junction diode cannot meet specifications.

Yet if this type of performance is required, either for purposes of high current
(read low resistance ) or high frequency applications then a different type of diode is needed.

This is the P-I-N or N-I-P diode. The I stands for “intrinsic”. This diode has a heavily doped p region and n region, just like in a ordinary pn diode. However, the resemblance ends there. In a P-I-N diode there is a high resistivity ( or
“intrinsic” region) sandwiched between the n and p heavily doped regions. The inclusion of the intrinsic or high resistivity region imparts some very useful characteritics to this structure. These characteristics are explored heuristically in this post.

Resistance: The resistance of the P-I-N diode is inversely proportional to the forward current through the diode and can be controlled by it. Very flat resistance characteristics can be generated this way. The reason for the low resistance with current is that as the high resistive region has very few carriers for recombination, any injected minority carriers coming from the heavily doped p and n regions do not die quickly but persist for “long” lifetimes in the I region. Thus the higher the current, the more free carriers in the I region and the lower the resistance. In the ultimate limit the forward resistance reaches the contact resistance which can be made very low.

Capacitance: The pn junction zero bias capacitance in the P-I-N diode is very low ( or relatively low compared to the ordinary pn junction diode). The reason is that the depletion region ( the region that is completely depleted of carriers with increasing reverse bias or zero bias) forms the “insulator” of a parallel plate capacitance. The parallel plates are, of course, the heavily doped p and n regions of the diode. The higher the resistivity of the I region the wider the depletion region and the lower the capacitance. Also the capacitance is very flat over a wide band of high frequencies so matching with other circuits becomes easier. As a result of the low capacitance the P-I-N diode can switch very fast and can be used in high frequency applications.

Reverse breakdown voltage: The breakdown voltage is high since the breakdown electric field drops voltage across a wider depletion region. As the depletion region becomes wider and wider with reverse voltage the breakdown increases.

Thus if one wants to reconcile high breakdown with low resistance and low capacitance then a P-I-N diode is a great choice. Both power diodes and RF diodes can be made with this technology.

Some disadvantages in the usage of the P-I-N diode are that (a) Its performance can only be predicted accurately if the lifetime of the minority carriers in the I region are known accurately. There are not a lot of analytical techniques to calculate this, therefore for precise usage, measurements need to be made. ( See the previous posts). (b) Most circuit simulator programs such as PSPICE do not provide a mathematical model ( empirical or physics based) so circut simulation is difficult. (c) The fabrication of the diode is slightly more complex. However most vendors provide the parameters and application notes for their P-I-N diodes so usage is made fairly easy. However, designing one from scratch can be quite involved because of the above factors.


SPG designs, develops and delivers custom analog and RF/wireless asics and modules.

FPGA Design and development service

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A wideand RF detector ( 40 Mhz to 3 Ghz) -75 dBm to 5 dBm input

A wideband RF detector

A wideband RF detector

Linear detector performance

Linear detector performance curves

A wideband linear RF detector

Price for one unit: $25.00. Lead time for delivery 3 days. 30 Day return policy. Pricing for 100 units or more: $20.00 per unit.  Please contact Signal Processing Group Inc. for details for purchase from Signal Processing Group Inc. Email: 24/7

Wideband RF detector perforamce , more details

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2 stage 35 dB gain RF amplifier. Front of the module

Full range frequency response

2 stage amplifier deta

Please see details at    Delivery lead time is 3 days. Return within 30 days for a full refund. Price is $15.00 for one unit and $10.00 per unit in volumes of 100. For higher volumes than 100 please contact Signal Processing group Inc.

miniature LNA module

Mni LNA performance

Delivery lead time is 3 days. Return within 30 days for a full refund. Price is $15.00 for one unit and $12.00 per unit in volumes of 100. For higher volumes than 100 please contact Signal Processing Group Inc. at email: or call 602-626-0272 for fastest service.

A high frequency divider from 500 Mhz to % Ghz+

The input interface.
The frequency divider has a differential analog interface. The following parameters apply:
The minimum frequency that can be input is 500 Mhz and the maximum frequency is 6.0 Ghz.
The RF input level is 5 dBm to – 5 dBm. For lower frequencies make sure that the slew rate is
greater than 560 V/us. The input is biased by two 500 Ohm resistors connected to a 1.6V DC bias.
Therefore AC coupling is used at the input. These are two 100pF capacitors.
The output interface.
The output is single ended. The output driver is capable of sourcing and sinking 24 mA. The
equivalent output impedance is 50 Ohm. To avoid reflections it is recommended that the divider
work into a 50 Ohm load.
General operation.
The inputs are applied to the input SMA I/O. The product will work with both a differential input as
well as a single ended input. However, a differential input works best. The division ratio is applied
to the N1 and N2 control inputs as follows:
N2 N1 Division ratio
0 0 8
0 1 16
1 0 32
1 1 64
The logic levels are:
Logic level Voltage
1 1.4V minimum
0 0.6V maximum
The supply voltage interface.
The operating supply voltage is 3.3V typical. The quiescent (DC) operating supply current is 2 mA.

A high frequency divider 500 Mhz to 5 Ghz+

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SPDT DC to 3 Ghz RF switch

DC to 3 Ghz RF SPDT switch

RF Switch typical features

Supply voltage = Vcc = 0/+5 Vdc
Operatng temperature = TA = -50° C to 125 Deg C
Operating impedance = 50 Ohm
Input power for 1 dB
compression ( 5.0V system) = 37 dBm ( f = 0.5 to 3 Ghz)
Input third order Intercept = 64 dBm ( 0 to 5.0V system, f = 0.5 to 3 Ghz)
Operating frequency range = DC to 3 Ghz.
Insertion loss DC to 3 Ghz = 0.8 dB
Isolation DC to 3 Ghz = 14 dB minimum
Return loss DC to 3 Ghz = 20 dB
50% contl to 10/90 %
( ON/OFF) = 120 ns

A single stage RF amplifier as a gain block

A single stage RF amplifier summary specifications

Summary Specifications

Gain,  Operating: 19.5 dB
Operating frequency range: 1.0 – 2700 Mhz
OIP3: (Pout = 19.0 dBm),  -8.5 dBm
P1dB: 4.6 dBm
N.F: 4.2 dB
Supply voltage Operating: 3.3  – 5.5 Volts

Price: single unit $7.50, 100 units : $5:50.

Free delivery, shipping lead time 2 days.

30 day return policy, buyer ships.
Supply current Supply = 5.0V,  23.0 mA

Embedded design and development

Signal Processing Group Inc. is offering embedded design and development using Microchip processors. Please contact us on for more information

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