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35 votes
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Why isn't the BIOS' ROM chip made using CMOS technology?

You're mixing up implementation technology with colloquial terms for functionality. CMOS - Complementary Metal Oxide Semiconductor - is a method of making logic and related circuitry using both N-...
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31 votes
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Why do CMOS NOT gate designs differ from BJT NOT gate designs?

However, I've always been perplexed as to why people do not use the former method for chip manufacturing. In chip design, resistors take up more area than transistors, and area is one of the main ...
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30 votes
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Why do we use a CMOS for inverting a circuit when the PMOS already achieves that?

In a word: Efficiency. You can use a PMOS transistor to drive a logic output high (e.g. VDD) when the input is low (e.g. GND). However, you can't use that same PMOS transistor to drive a logic output ...
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29 votes
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Why is there no rolling shutter when using a mechanical shutter?

When I have a camera, that can take still images at 10fps with a mechanical shutter, why doesn't it mean the sensor can take images at 10fps electronically without producing rolling shutter? In order ...
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27 votes
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Why have both: BJT and FET transistors on IC output?

Paragraph 2 of the description says: FAN3100 drivers incorporate MillerDriveTM architecture for the final output stage. This bipolar-MOSFET combination provides high peak current during the Miller ...
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26 votes
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Can I connect two microcontrollers via RS232 separated by a distance of 3.5 inches? Both are on two separate PCBs

If the distance is really 3.5 inches, it is quite absurd to think that when connecting two UARTS together you must use RS-232 tranceivers. You don't need to use RS232 tranceivers and you don't need ...
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24 votes

Can a NOT gate be used to achieve 180 degree phase shift?

What is 180 degrees phase shift? When the signal is a sine wave, a 180 degrees phase shift delays the signal for half the period of that sine wave, the sine wave then looks inverted: Can an inverter ...
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24 votes

Do MOSFET logic gates necessarily need an N channel MOSFET?

Couldn't it be replaced with a simple resistor into ground like this? Yes it can and is has been done: PMOS logic there's also the complementary version: NMOS logic We've been there and done that! So ...
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23 votes
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Why do we need NMOS transistors for NAND gate?

if X or Y on both PMOS transistors is 0 , then both transistors will be open and the output will be 0 because there will be no flow of the current. The output will not be '0', it will be floating. ...
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23 votes

Why do CMOS NOT gate designs differ from BJT NOT gate designs?

It's possible to build this circuit with 2 BJT's or one MOSFET You're reading too much into it. The difference isn't the technology of the transistor, it's method of circuit operation In the first ...
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21 votes
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Why is a capacitor used to protect CMOS chips?

That's not a protection device, if you intend "protection" as something that prevents the chip to die, but it serves as a so-called bypass capacitor. It acts as a reservoir of energy whenever the ...
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20 votes
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Can unconnected inputs make an IC get warm?

Yes, CMOS circuits can get hot when there are floating inputs. You should always connect unused CMOS input pins to a defined voltage, usually GND or Vdd, unless the datasheet tells you otherwise (see ...
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20 votes

Why do CMOS NOT gate designs differ from BJT NOT gate designs?

Your circuit with the bjt is RTL (resistor transistor logic). There’s DTL, TTL, ECL, PMOS, NMOS and CMOS. There’s others as well, but you can research these if you’re interested. Basically there’s a ...
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19 votes

Why is there no rolling shutter when using a mechanical shutter?

There are two parts to this: First, rolling shutter can still occur with (some, see note) mechanical shutters. However, this is only at short exposure times. The shutter is built out of two curtains. ...
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18 votes
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What does the dashed line between diodes in a CMOS protection network mean?

The dashed line means that the diode is actually distributed across the resistor structure. The resistor is made using a doped region in the silicon, and there is an inherent PN junction between this ...
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18 votes

Why do we need NMOS transistors for NAND gate?

You make the common, and mistaken, assumption that a node that is not actively driven (has zero current flowing) must be at a low voltage. That is not true. The output of the gate must be pulled down ...
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16 votes

How to manufacture chip on board?

A custom chip for 10k units is unlikely to be cheap, as the masks will almost certainly cost more than $1k, which means your chip cannot possibly be made for $0.10. The reason the one you've found ...
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16 votes

Why does switching cause power dissipation?

Consider a MOSFET switching. Switching is a transient event, so losses are not usually modeled as "power". Each switching action dissipates a bit of energy. Then you multiply this by the ...
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  • 60k
14 votes

Why isn't the BIOS' ROM chip made using CMOS technology?

Back when the PC was first invented, most of the logic on it was power-hungry NMOS and TTL chips. CMOS was very new and the only circuits in the PC that used it were associated with things that ...
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14 votes
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MOSFET construction

If a very large MOSFET (i.e. with a very wide channel) was implemented as a single physical device, like the one you saw in class, then the gate electrode would be very long and thin. This would cause ...
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14 votes
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pull-ups between logic gates

This is a case of interface between logic families (from LS-TTL -to- CMOS). Although both are powered from +5v supply, logic levels differ: Logic low output for the 74LS93 is compatible with logic ...
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13 votes
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Using CMOS Schmitt trigger inverters in quartz crystal oscillator circuit

A Schmitt trigger inverter is a bad idea for the first inverter which is driving the crystal directly. It may not even oscillate at all as shown, or oscillate at some undesired frequency. Note ...
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13 votes

Why does decreasing the CMOS supply voltage also decrease the maximum circuit frequency?

Decreasing the voltage decreases the maximum frequency that can be used such that the operation of the digital system is as desired. This is because the equivalent resistance, \$R_{eq}\$, of the CMOS ...
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  • 2,411
13 votes

Can I connect two microcontrollers via RS232 separated by a distance of 3.5 inches? Both are on two separate PCBs

No, your microcontrollers will not communicate using RS-232 unless you're using RS-232 levels, which only your second option does. What you mean with (RX, TX, CTS and RTS lines) is that they're ...
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12 votes
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Precise differences between DRAM and CMOS processes

Here is a (slightly dated) paper that discusses the differences: http://www.ece.neu.edu/faculty/ybk/publication/ASSESSING_MERDRAM_ELSEVIER.pdf Basically, it boils down to a few important differences. ...
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11 votes

Is the NAND logic gate perfectly symmetrical?

Depends on the environment. Maybe in your circuit above and in an FPGA they are the same but in an ASIC library you find differences between the various inputs.
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11 votes

Why have both: BJT and FET transistors on IC output?

The CMOS and BJT output stages are combined to from one stage, the manufacturer calls this a "MillerDrive(tm)". Why they do this is explained in the datasheet: My guess is that they want to achieve ...
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  • 78.8k
11 votes

Can I connect two microcontrollers via RS232 separated by a distance of 3.5 inches? Both are on two separate PCBs

One thing not mentioned in the other answers, is that not only you don't need RS232 transceivers at such a short distance and so low speed, but the use of flow control signals is also a waste of MCU ...
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10 votes
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Is the NAND logic gate perfectly symmetrical?

There will be a very small difference in that circuit because of the differences in VGS in the N stack while the circuit is sinking current during switching. M1 will be marginally slower than M2 under ...
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10 votes
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How Does an Adjustable Transistor Size CMOS Driver Work?

The approach to do this is alluded to in the datasheet snippet you linked, which mentions "fingers", or separate parallel gates in a wide MOSFET that forms the output driver. These fingers ...
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