22 Questions
What is the figure of merit of a digital IC?
Product of speed and power
How is speed specified in the figure of merit?
In terms of propagation delay time expressed in nano seconds
What happens to power dissipation if high speed is desired in a digital circuit?
It increases
What is the figure of merit of a digital IC and how is it calculated?
The figure of merit of a digital IC is the product of speed and power, calculated as: $Figure of merit = Propagation time (ns) imes power (mW)$.
Why is a low value of speed-power product desirable in a digital IC?
A low value of speed-power product is desirable because it indicates that the digital IC has low power dissipation while maintaining high speed or low propagation delay.
What happens to power dissipation if high speed or low propagation delay is desired in a digital circuit?
If high speed or low propagation delay is desired in a digital circuit, there will be a corresponding increase in power dissipation, and vice-versa.
What is the purpose of a sample and hold circuit?
To create samples of voltage given as input and hold these samples for a definite time.
What is the sampling time range for a sample and hold circuit?
Between 1µs to 14 µs
What is the role of a sample and hold circuit in digital communication?
To convert analogue signals into digital signals by taking samples of the analogue signal.
How is the holding time of a sample and hold circuit defined?
As the time duration during which the circuit holds the sampled value.
How is a sample and hold circuit implemented using operational amplifiers?
By connecting two OPAMPS via a switch, where one is used for sampling and the other for holding.
Why is a sample and hold circuit needed in digital communication?
To mitigate the noise interference in analogue communication and convert analogue signals to digital signals.
What are the main components of a sample and hold circuit?
N channel Enhancement type MOSFET, a capacitor, and a high precision operational amplifier
How does the N-channel Enhancement MOSFET function in a sample and hold circuit?
It acts as a switching element, with the input voltage applied through its drain terminal and the control voltage applied through its gate terminal.
What is the role of the capacitor in a sample and hold circuit?
The capacitor stores and holds the electric charge fed to it during the holding period.
What is the significance of the high impedance operational amplifier in a sample and hold circuit?
The high impedance operational amplifier prevents the capacitor from discharging, leading to the holding of the charge for a definite amount of time.
What is the sampling rate of an Analog-to-Digital Converter (ADC) measured in?
The sampling rate is measured in 'samples per second' (SPS) or Hz if using sampling frequency.
How does the sampling rate of an ADC impact its ability to handle frequencies?
The more samples the ADC takes, the higher frequencies it can handle.
Why are ADCs important in digital systems dealing with real-time signals?
ADCs are important for accurately reading real-time signals and providing vital information, especially with the rapid development of IoT for everyday life applications.
What is the relationship between the holding period and the output processed by the operational amplifier in a sample and hold circuit?
The holding period is when the output processed by the operational amplifier occurs.
How is the control voltage used to switch the N-channel Enhancement MOSFET in a sample and hold circuit?
When a positive pulse of the control voltage is applied, the MOSFET is switched to the ON state, acting as a closed switch. When the control voltage is zero, the MOSFET is switched to the OFF state, acting as an open switch.
What is the role of the N-channel Enhancement MOSFET when it acts as a closed switch in a sample and hold circuit?
When the MOSFET acts as a closed switch, the analogue signal applied to it through the drain terminal is fed to the capacitor, causing the capacitor to charge to its peak value.
Study Notes
Figure of Merit of a Digital IC
- The figure of merit of a digital IC is defined as the speed-power product, which is measured in picojoules (pJ).
- Speed is specified in the figure of merit as the propagation delay, which is the time taken for a signal to pass through the circuit.
- A lower value of speed-power product is desirable in a digital IC as it indicates a more efficient circuit.
Power Dissipation and Speed
- If high speed or low propagation delay is desired in a digital circuit, power dissipation increases.
- This is because high-speed circuits require more power to operate.
Sample and Hold Circuit
- A sample and hold circuit is used to sample an analog signal and hold it constant for a certain period.
- The sampling time range for a sample and hold circuit is typically in the range of microseconds to milliseconds.
- The role of a sample and hold circuit in digital communication is to convert analog signals to digital signals.
- The holding time of a sample and hold circuit is defined as the time for which the circuit holds the sampled value.
- A sample and hold circuit can be implemented using operational amplifiers.
Components of a Sample and Hold Circuit
- The main components of a sample and hold circuit include an operational amplifier, a capacitor, and an N-channel Enhancement MOSFET.
- The N-channel Enhancement MOSFET functions as a switch in a sample and hold circuit.
- The capacitor is used to store the sampled value.
- The high impedance operational amplifier is used to amplify the sampled signal.
Analog-to-Digital Converter (ADC)
- The sampling rate of an ADC is measured in samples per second (S/s).
- The sampling rate of an ADC affects its ability to handle frequencies, with higher sampling rates required for higher-frequency signals.
- ADCs are important in digital systems dealing with real-time signals as they convert analog signals to digital signals.
Sample and Hold Circuit Operation
- The control voltage is used to switch the N-channel Enhancement MOSFET in a sample and hold circuit.
- When the N-channel Enhancement MOSFET acts as a closed switch, it allows the capacitor to charge and store the sampled value.
- The holding period is the time during which the output is processed by the operational amplifier in a sample and hold circuit.
Test your knowledge about the figure of merit of digital ICs, which is defined as the product of speed and power. Learn about the trade-offs between speed, propagation delay time, and power in digital circuits.
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