analog IC interview

Analog Integrated Circuit Interview question

1) Differentiate between Analog and Digital IC design ?
Analog circuit design is different from Digital Circuit design in following aspects:
• Layout is critical since the routing should be done according to RF design rules
• Layout in digital can be completely automatic which is not the case in analog
• Grounding issue is critical in Analog or RFIC compared to Digital IC
• Size of analog IC’s are large compared to digital since it comprises of inductors capacitors and resistors where as digital IC’s includes only capacitors and resistors.

2) Which are the various processes used for fabrication of IC’s?
The different processes used for fabrication of IC’s are:
• GaAs
BiCMOS_ should know some fundamentals on each process

3) What is the basic purpose of using EM simulation?
Basic purpose of EM simulation is to predict the actual behavior of RF Circuits considering all the parasitic and coupling. This is not considered in circuit simulation.

4) List the instruments required for testing RF Modules and IC’s Instruments required for RF testing are:
• Spectrum Analyzer
• Vector Network Analyzer
• Noise Figure Meter
• Power Meter
5) Which are basic blocks that comprise the RF Transceiver?
RF Receiver consists of
• Low Noise Amplifier/RF Amplifier
• Mixer
• Local Oscillator
• Demodulator
• Automatic Gain controller
• Automatic Frequency controller.
• Filters
• Switch

RF Transmitter consists of
• RF power amplifier
• Modulator
• Carrier Oscillator
• Filters
• Switch

6) What is the basic function of a power amplifier?
The main function of RF power amplifier is to boost the power level of a Signal so that it can travel a significant distance. Power amplifiers are required in all the transmitters

7) What is the basic function of a low noise amplifier?
The main function of Low Noise Amplifier is to amplify the weakest possible Signal with Noise Figure as low as possible during reception and to improve the sensitivity and dynamic range of a receiver.

8) What is the basic function of a Mixer?
Frequency translation is the key role of Mixer. Output contains the sum or difference of two frequencies i.e. RF frequency and LO(Local Oscillator)

Some Good Books:
• CMOS Circuit design, layout and simulation, R Jacob Baker, Harry W. Li and David E. Boyce.
• Analog Integrated Circuit Design, David Johns, Ken Martin,
• CMOS Analog Circuit Design, Phillip E. Allen and Douglas R. Holberg,
• Design of analog CMOS Integrated Circuits, Behzad Razavi,
• RF Microelectronics, Razavi
• RF microelectronics Thomas Lee
• Any Digital books may be rabey

Typical questions

1 Gain, (how to improve gain?)
2 Bandwidth, (how to improve bandwidth?)
3 Feedback,(Stability is a must ask question! Know pole, zero, gain and phase margin!)
4 Slew rate,(How to improve slew rate?)
5 Offset,(how to eliminate offset? Chopper stabilized circuits, auto zero)
? Noise,(what is thermal, flick, shot noise? Or noises of MOSFET? (How to reduce noise)
6 Compensation (what is Miller, lead and Lag compensation?
7 Layout (centroid, interdigital) (how to improve the match of current mirror,
differential pairs?, Same surroundings(dummy transistors) and Common-centroid geometry (fingers, interdigitated fingers, what is the purpose of breaking into fingers?
8 Thermal resistance (basic calculation).
9 Filter
10 Oscillator
11 Peak detector
12 Frequency divider
13 Bandgap Reference
14 PLL and its functions