NAND is an abbreviation for “NOT AND.”
What is a NAND gate?
A two-input NAND gate is a digital combination logic circuit that performs the logical inverse of an AND gate. While an AND gate outputs a logical “1” only if both inputs are logical “1,” a NAND gate outputs a logical “0” for this same combination of inputs. The symbol and truth table for a NAND gate is shown in Figure 1. The Boolean expression for a NAND gate with two inputs (A, B) and output X is:
Figure 1. Symbol and truth table for NAND gate
What are NAND gates used for?
NAND gates help detect if a single input to a digital system has gone low. For example, a simple security system consisting only of NAND gates could be used to monitor the status of sensors connected to windows and/or doors. If a window/door is closed, the sensor sends a logical “1” signal to the security system. While all windows and doors are closed, the alarm output is “0.” If a single window or door is opened, the security system output changes state to become “1” and this can be used to trigger an alarm or take some other action.
The popularity of the NAND gate is derived from the fact that it is the easiest of the digital logical operators to implement using transistor technology, e.g., a two-input NAND gate uses only four transistors when implemented in CMOS. All other logical operators can be implemented using only NAND gates connected in different configurations. Early microprocessors were implemented using only this trivial circuit.
|Nickel Metal Hydride||请参考：NiMH|
|Non Return To Zero||请参考：NRZ|
|Non-Interruptible Power Supply||请参考：电池备份|
|Non-Inverting Op Amp||
A non-inverting op amp is an operational amplifier circuit with an output voltage that is in phase with the input voltage. Its complement is the inverting op amp, which produces an output signal that is 180o out of phase.
What is a non-inverting input?
An amplifier’s non-inverting input refers to the pin configuration. The non-inverting input is the terminal marked with a plus (+) sign, and the inverting input is marked with a minus (-) sign. These can also be referred to as positive and negative terminals.
Circuit diagram symbol for an op amp with non-inverting (+) and inverting (-) inputs.
What is the formula for a non-inverting amplifier?
Non-inverting op amps work following the op amp golden rules:
Non-inverting op amp circuit.
Consider the non-inverting op amp circuit shown above. According to the Voltage Rule, the voltage at the inverting (-) input will be the same as at the non-inverting (+) input, which is the applied voltage Vin.
The current going through R1 can then be given as Vin/R1.
According to the Current Rule, the inputs draw no current, so all that current must then flow through R2.
The output voltage can then be given as Vout=Vin+(Vin/R1)R2.
The gain is then Vout/Vin=1+(R2/R1).
The gain will never be less than 1, so the non-inverting op amp will produce an amplified signal that is in phase with the input.
What is the difference between an inverting and non-inverting amplifier?
A non-inverting amplifier produces an output signal that is in phase with the input signal, whereas an inverting amplifier’s output is out of phase. Both the inverting and non-inverting op amps can be constructed from one op amp and two resistors, just in different configurations.
Learn More: Operational Amplifiers (Op Amps)
|Non-Volatile Power Supply||请参考：电池备份|
A notch filter is a type of band-stop filter, which is a filter that attenuates frequencies within a specific range while passing all other frequencies unaltered. For a notch filter, this range of frequencies is very narrow.
The range of frequencies that a band-stop filter attenuates is called the stopband. The narrow stopband in a notch filter makes the frequency response resemble a deep notch, which gives the filter its name. It also means that notch filters have a high Q factor, which is the ratio of center frequency to bandwidth.
What kind of filter is a notch filter?
A notch filter can be either active or passive depending on the design. A passive filter is one made of only passive elements, i.e. resistors, capacitors, and inductors. Active filters contain an amplifying element, such as an op amp, which is used in some notch filters.
What is a notch filter used for?
Notch filters are used to remove a single frequency or a narrow band of frequencies. In audio systems, a notch filter can be used to remove interfering frequencies such as powerline hum. Notch filters can also be used to remove a specific interfering frequency in radio receivers and software-defined radio.
How do you make a notch filter?
Notch filters can be created from a combination of low pass and high pass filters. See App Note 431: Switched-Capacitor IC Forms Notch Filter for one method of making a notch filter using a Switched-capacitor filter (SCF).
|NTSC||由国际电视标准协会于1953年制定的彩色电视标准。NTSC的主要特点是在1941年制定的黑白电视标准的基础上添加了彩色功能, 这样, 原来的黑白电视仍可保证正常工作。
(NTSC的另一特点是对相位精度的依赖性很强，即在信号传输和处理过程中很难保持色度。电视工程师常常戏称为“Never Twice the Same Color (从不重色)”)。
彩色副载波的参考频率是3.579545MHz，行同步(H)在黑白电视标准15.750kHz的基础上稍作调整，使彩色副载波的频率是行同步时钟的455/2倍。场同步频率为：Fv = Fh x 2/525。