PIN Photodiode as high precision current source switch

[CVT]

precision current source

Hi Everyone

I have not being a member of edaboard for a long time so please inform me if I can place this post in a better place. I thought that this would be a good place since PIN diode are used a lot in RF applications, although this is not an RF application.

MY NEED
I need a good source of information (Technical or Application notes) on PIN Photodiodes. I have searched in google with no success. I would also like to know where I can get a hold of a spice model. Are there companies that provide spice models for PIN Photodiodes? I suspect that I will have to create my own model from a datasheet and for that I will need to a good understanding of how these diodes work. The control signal (optical input) will be a 100 ns pulses a rate varying from 10Hz to 5 Mhz.

I have identified the PC1-6 as the best candidate thus far for my application, low leakage current. **broken link removed**

BACKGROUND
I want to use it in a design as a VERY accurate, EXTREMELY “low leakage current” current source. The reason for it being a Photodiode is so that I can control it (on/off @ fixed on current) with an optical feedback signal. I want to use it to discharge a capacitor in a Charge Recycling Integrator circuit. This type of circuit is used to integrate charge (current) over a very wide dynamic range form 10pA to 10uA. It is clear that with a 10pA signal current flowing into the charging capacitor a leakage of say 50 pA from the supposedly of current source connected to it will give large errors. I have considered usin silicon switches (MESFETS) to connect a current source to the capacitor to discharge it but these cause even bigger errors at low current measurements due to the large injection charges when the MESFET switches.

Any help will be much appreciated

Thanks
Chris

 

[maniana]

precision current source circuit

as far as I know there is no such thing like a Spice model of a PIN diode.
The reason for that is that Spice does not model carrier lifetime or carrier transition time in the I-region (or something like that, I am not a semiconductor expert but I was looking for a PIN diode model sometime ago and I read this in some application note).

see page 2-4, "Modeling" of this:
**broken link removed**

 

[biff44]

photodiode spice model

I do not understand your initial post. When I type in "SPICE Model of P-i-N Photodiode" I get 10 pages of hits.

 

[maniana]

pin photodiode spice model

Hi,
As I said , I am not an expert, but if you look at the results of "SPICE Model of P-i-N Photodiode" search, you will see that these are "hand created" models.
As far as I understand these are not built in spice models.
a standard diode model is a built in model while models that you get from internet are "subcircuits" created by people to model phenomena that is not modelled by a standard spice model. spice has only a diode model that does not have parameters that are important in order to model the pin-diode behaviour accurately. if you take a spice manual and look at the diode model parametrs you will see that there is no such parameter like "carrier lifetime" hence people create those subcircuits to model this parameter, and this model may or may not reflect the actual diode that you intend to use.
It all depends on the accuracy you need.
You would need to measure your diode and then CREATE a model that fits your measurements.

 

[FvM]

high precision photo diode

I can't follow your view on "hand created" versus built-in models. Both are empirical to some extent.

On the other hand, for all device properties, that are not represented in SPICE standard models, equivalent circuits or analog behaviour descriptions are the most simple ways. Of course, you can also add user model code, if you have a version, e.g. original Berkley SPICE, that has the option. But this would be interesting rather to increase speed than achieve better accuracy. As far as I experienced, anything can be modelled as analog behaviour.

The real problem is to get correct model parameters for your device. If you want to measure it's behaviour first and extract a model, why not build your intended PIN diode circuit, make some measurements and you're done. What's the particular purpose of simulation in this case?