How to decide CMOS or bipolar?

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Hi Freaks,
How do chip designers decide to go bipolar or CMOS on a BiCMOS chip? I mean if you have a chip as shown in the pic. below which has a number of peripherals including the core how do they select CMOS or bipolar? Is it as simple as drive and power (bipolar) vs. speed (CMOS)? Of course I understand the core would be primarily CMOS but what about the peripherals?

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Each technolgy has its good points and bad points. Bipolar is usually faster but more power hungry whereas CMOS is lower power and higher density. As per your example - where does it mention that it is BiCmos?

You could implement the core in bipolar if you wished, but it would suck more power and take more silicon area. It would also be faster. If the aduc device is BiCmos, most of the logic would be cmos and maybe some of the specialised analog parts would use bipolar.

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I think that the Xmega is definitely bipolar; at least how it affects me: The bouts of euphoria with new announcements and possibilities alternate with the lows of no product and long errata list...

Quote:
Mania symptoms may include excessive happiness, excitement, irritability, restlessness, increased energy, less need for sleep, racing thoughts, high sex drive, and a tendency to make grand and unattainable plans.

Yep, go through the Xmega threads and tell me which of those symptoms do not apply.
Quote:
Depression symptoms may include sadness, anxiety, irritability, loss of energy, uncontrollable crying, change in appetite causing weight loss or gain, increased need for sleep, difficulty making decisions, and thoughts of death or suicide.

I guess only the most ardent 'Freak will have the last listed symptom. ;) But you can all see that the Xmega is definitely bipolar.

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Analog Devices has one of the best processes for mixing CMOS and bipolar (of the unemotional silicon kind).

Bipolar tends to be "better" for analog (amplifiers) where input offsets are more stable and predictable. Its really hard to hold the MOS gate threshold at very precise values which is what you need for a DC stable amplifier.

But, CMOS gives you very nice analog switches and lower joules per circuit node per logic transition.

If you need really high speeds, then neither works well (though bipolar tends to extend to higher frequencies a bit easier than CMOS). Upper speed end in MOS tends to require shift to GaAs while bipolar can continue upwards in frequency for a while.

So, its a really mixed bag. It depends a LOT on what the company's design and fab capabilities are, what the design goals are, what the cost point is, Further, two companies after the same design goals may choose very different ways to get there.

Looking at that promo in the original post, Analog Devices is really stretching things when they call those "Precision Analog Microcontroller". Delta-sigma converters require an integrator and a comparator - those are about the only "analog" things on the chip and they can be done well in CMOS. The DACs need good analog switches and good trimming, both of which AD has good processes for (in CMOS). Timers, PWM, UART, SPI, I2C, ARM7, SRAM, FLASH, are all CMOS. I would expect very little, if any, bipolar on those chips.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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That makes sense, Jim. Xmega is "mega- bipolar".

I just think the ability to mate CMOS and Bipolar and get it working is amazing. Coming from the process side, I have seen way too many issues after bringing the technologies together.

Do you know of any chips which have only CMOS or only bipolar (not the Xmega kind..)?