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42

CMOS (complementary metal oxide semiconductor) logic has number of desirable characteristics: High input impedance. The input signal is driving electrodes with a layer of insulation (the metal oxide) between them and what they are controlling. This gives them a small amount of capacitance, but virtually infinite resistance. The current in or out of a ...


33

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-Channel and P-Channel field effect transistors. One of its defining characteristics is extremely low static power consumption - power is almost only used when ...


29

It is generally a good idea to include a gate resistor to avoid ringing. Ringing (parasitic oscillation) is caused by the gate capacitance in series with the connecting wire's inductance and can cause the transistor to dissipate excessive power because it doesn't turn on quickly enough and hence the current through drain/source in combination with the ...


28

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 low when the input is high. When you drive the input high in your PMOS inverter, it turns off, leaving the output effectively high-impedance, which is not ...


27

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 plateau stage of the MOSFET turn-on / turn-off process to minimize switching loss, while providing rail-to-rail voltage swing and reverse current capability. ...


26

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 to understand why, we have to take a look at a typical 3T(ransistor) pixel: This 3T pixel can be used with rolling shutters, but not with (electronic) global ...


24

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 do this? No, because it has signal gain, the output would be a square wave, not a sine. When the signal is a square wave with a 50% duty cycle, then something ...


20

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 chip draws pulses of current when switching occurs. If the power rails were truly ideal connections, with no resistance nor inductance, bypass caps wouldn't be ...


20

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 also the end of this answer and Michael's answer). If a pin could be configured as either input or output and you are not sure which it will be, then you could ...


19

It refers to how the gates are constructed on the IC. CMOS stands for Complementary MOS (metal oxide semiconductor), which uses uses both PMOS and NMOS (i.e. complementary) to construct the logic. CMOS is fast, has a large fan out and uses less power than other technologies. Other families are TTL (transistor-transistor logic, NPN/PNP still used), ECL (...


16

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. Before the exposure, curtain 1 is in front of the sensor. When the exposure starts, curtain 1 moves down (or up or whatever) and starts exposing the sensor. At ...


16

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 costs $0.10 is because they sell in a much greater volume (100k-millions), so the cost of masks and setup for a production run is spread over many more units. ...


15

Oli and Olin have explained the strengths of CMOS, but let me take a step back. TL:DR: Complementary logic allows a rail-to rail output voltage swing, and MOSFET transistors are a very scalable technology (billions of transistors can be obtained on a small surface) with some very useful properties (compared to BJT). Why CMOS? The need for complementary ...


14

MSalters answer is 80% correct. The estimate comes from the average power necessary to charge and discharge a capacitor at constant voltage, through a resistor. This is because a CPU, as well as every integrated circuit, is a big ensemble of switches, each one driving another one. Basically you can model a stage as a MOS inverter (it can be more complicate, ...


14

Fundamentally, a buffer is an amplifier. It takes a small signal (lightly loading the source of the signal) and provides a copy of that signal that can drive a heavy (e.g., capacitive) load. They are used in places where connecting the heavy load directly to the source would adversely affect the signal. Such effects arise because the signal source has a ...


14

I would say its the width of the exposed part of the sensor: you can have a slit that is 1mm move across the sensors, or 10mm, etc. Probably useful to write as a ration, 10% of the sensor width/height. Added: RM What Sandos said above. Expanding on that. A rolling shutter (Wikipedia) is a camera (or image) sensor technique that produces exposure times ...


14

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 a significant RC delay down the gate and so the MOSFET would turn on and off very slowly. Furthermore, it would be difficult to put such a device in a package ...


13

TL:DR It's for obtaining the right driving strength, the right input capacitance and the lowest latency. Explanation Logically there is no difference between one or three inverters, but... This kind of buffer is made to drive a higher load than just a single inverter, and this has to do with speed. The problem is that a CMOS gate can drive a current ...


13

No, the circuit structures to produce gates in TTL and CMOS are very different. It's actually a very complex topic, because at this level, you can't just treat transistors (BJTs or FETs) as simple "switches". It becomes an analog circuit design problem in which many issues need to be considered: how static and dynamic currents flow, where charges are stored ...


12

The first comprehensive logic series was the TTL series 74xx. This used BJTs (Bipolar Junction Transistors). Later there came variants like the often used 74LSxx, where the "LS" stands for Low-power Schottky TTL. As the name implies these used less power than the rather power-hungry TTL, and were faster too. At the same time the CMOS 4000 series was ...


12

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 resistor R1. That is supposed to bias the inverter as a linear amplifier close to the middle of its output range. The little bit of noise generated by the inverter ...


12

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 needed to run on battery when the power was off, such as configuration RAM and the real-time clock. Nowadays, nearly all of the logic is CMOS, including the power-...


11

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. Leakage current. The pass transistors for the DRAM cells must be extremely low leakage, otherwise the leakage current will affect the bit stored in the ...


11

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.


11

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 a certain (output drive) performance that cannot be achieved by only using CMOS transistors or only using the NPNs with the manufacturing process that they're ...


10

It is very likely CPU's and SoC's are used by hardware description languages like Verilog and VHDL (two major players). These languages allow different levels of abstractions. In VHDL, you can define logic blocks as entities; it contains inputs and output ports. Within the block you can define the logic required. Say you define a block with input A, input B ...


10

No, if the nMos is on, that means it conducts. If it conducts, it is a low resistance (ideally zero). That creates a conductive path to ground, bringing the output to that potential. Think of the two devices as being resistors controlled by voltage. If the upper resistor is shorted, the output is 5V. If the lower one shorted, the output is at ground.


10

You do not need a base resistor. Not only do MOSFETs not have bases (they have gates), but the gate is (very) high impedance. Except when the MOSFET is changing states, the gate current is essentially zero. It is common practice to place a resistor (the value isn't terribly critical -- anything between \$ 1k\Omega \$ and \$1M\Omega\$ will do) from the gate ...


10

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 some conditions. There are however likely to be other factors, say in how the circuit is laid out, that will have an equally large effect. Define perfect. ...


9

Notice how the top NPN can only make the output reach VDD-0.7 V, I assume it is the job of the mosfet to take care of the last 0.7 V. It looks as if the BJT's are doing most of the grunt work and the mosfets are taking care of making the output reach VDD and a strong GND. I could be wrong though.


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