differences between analogue and digital transistors in fabrication

[senam53]

I wanna know the differences and of course if there is photos to explain it , it's great
As, i tried to search the web on it but coudn't reach any thing.
thanx in advance

 

[alexan_e]

Transistor is by nature an analog device.
What we call a digital transistor is actually an analog transistor that has internal resistor from the input to the base and a (pull up/down) resistor between the base and emitter.
see the schematics in the link
**broken link removed**


Alex

 

[eladla]

The layout of a transistor is dependant upon the application.
Lets talk CMOS for a second here.
Basiclly, there is no real diff between an analog and digital transistor.
Analog transistors deal with intermidiate voltage levels (small signal), and Digital transistors only deal in two basic voltages - 0 or 1 (large signal).
i.e. digital transistors work with the largest possible signal margin, which is exactly the point of digital.

In layout, this means that although they are similar, digital devices require less care in layout then analog devices.
But ultimatly, they are both laid out the same.

 

[senam53]

Transistor is by nature an analog device.
What we call a digital transistor is actually an analog transistor that has internal resistor from the input to the base and a (pull up/down) resistor between the base and emitter.
see the schematics in the link
**broken link removed**


Alex

Thanks for that, but i have to make a report so it's great if there is more explanation ,more comparisons and how they work .
So if there is references , good sites or more info i'd be greatefull

 

[alexan_e]

I did a search using Google and i can't find any article on this, there are a few data sheets but the explanation is the same.
There is nothing special except that you don't have to connect the two resistors externally .

This new series of digital transistors is designed to replace a single
device and its external resistor bias network. The digital transistor
contains a single transistor with a monolithic bias network consisting
of two resistors; a series base resistor and a base−emitter resistor. The
digital transistor eliminates these individual components by
integrating them into a single device. The use of a digital transistor can
reduce both system cost and board space. The device is housed in the
SC−89 package which is designed for low power surface mount
applications.
• Simplifies Circuit Design
• Reduces Board Space
• Reduces Component Count

Alex

 

[LvW]

Quote eladla: Basiclly, there is no real diff between an analog and digital transistor.

Basically, there are no digital parts at all. In particular, there are no "digital transistors".
All parts and all circuits or subcircuits are - by nature - analog!
However, some of them are operated outside their linear regions - and that's digital operation.
A good example is the "digital" CMOS-inverter: It can be biased to operate as a linear amplifier!
Remember: Knowing the terms is the base of understanding!

 

[afham_kun]

I believe the different between analogue and digital transistors is rely on process recipe of the foundry or fabrication house, which public can't have easy access to the document without writing in formal with special reasons, due to trade secret.
However, we do understand this...as mentioned by

The layout of a transistor is dependant upon the application.
Lets talk CMOS for a second here.
Basiclly, there is no real diff between an analog and digital transistor.
Analog transistors deal with intermidiate voltage levels (small signal), and Digital transistors only deal in two basic voltages - 0 or 1 (large signal).
i.e. digital transistors work with the largest possible signal margin, which is exactly the point of digital.

In layout, this means that although they are similar, digital devices require less care in layout then analog devices.
But ultimatly, they are both laid out the same.

So, the point is, the foundry work on IP specially for digital transistor improvement (which related to process recipe), which basically to cater the weakness of the transistor when it is apply in digital circuit, such as leakage current, etc.

I think, this topic can really make into research topic with more specific to what kind of process and technology.:smile:

 

[dick_freebird]

The one blurb looks like it applies to a "discrete" switching
transistor product, and they have simply put the base shunt
and series resistors that you would use in a normal 2N2222
application, on the die. Woo-hoo. Science.

In a MOS process, digital always chases minimum channel
length and will do any kind of device construction trickery
to get "reliable" operation. LDDs (which also make a lightly
doped source, hurting gm and adding a variable to matching),
halo implants (improving hot carrier but elevating D-B
leakage), loosening the HCE drift requirement ("it's just
digital, allow 10% instead of 5% gm degradation").

An analog transistor tends to not be operated at minimum
channel and would prefer a more straightforward device
construction (KISS).