Qualcomm Interview Question Bank – Part 1

In the campus placement season, it is better if we get company specific questions to prepare for the selection process. So, to help you out, we have already posted Question Banks for some core ECE companies and now, let us look at the following questions asked in recent times in Qualcomm interviews. In general, according to many interview experiences, Qualcomm puts much of its focus on DSP (Digital Signal Processing). Let’s start with the questions now…

Q : What do you mean by a Schmitt trigger?

A : Schmitt trigger is a comparator circuit which is used to generate square wave of a particular duty cycle as an output. Basically, it uses some internal positive feedback to raise the threshold when the input is low and vice-versa. In simple words, Schmitt trigger produces maximum level if the input is greater than upper threshold value and almost zero level if input goes below the lower threshold value. It can be implemented on many devices like BJTs (Bi-polar Junction Transistors), 555 timers etc. but most commonly on op-amps (operational amplifiers) as follows,

 

 

 

Q : Explain the difference between Moore and Mealy state models.

A : Two basic models of state machines are the Mealy and Moore models. In Moore model, the output of the state machine depends only on the state whereas in Mealy model, the output of the state machine depends on state as well as the inputs. Also, any Moore state machine can be converted to Mealy state machine but vice-versa is not true.

Q : How will you generate a rectangular wave?

A : There are two ways for generating a rectangular wave – using Schmitt trigger circuit, and using a DAC (Digital to Analog Converter) along with a microprocessor having software delays of appropriate time period.

Q : When do we use IIR and FIR filters?

A : When the system response is infinite, we use IIR (Infinite Impulse Response) filters and when the system response is zero, we use FIR (Finite Impulse Response) filters. Moreover, when the linear-phase characteristics are of concern, FIR filters are used else IIR filters are used. FIR filters are used for higher-order tapping whereas IIR filters are used for lower-order tapping.

Q : What do you mean by knee voltage?

A : Knee voltage means the minimum voltage level (threshold) required for current conduction and is also known as threshold voltage.

Q : What is the cause of distortion in amplifier?

A : Distortion in amplifier is mainly due to the non-linearity of the device.

(Continued to Part 2…)

Gautam Vashisht