ECAD Service: Digital Signal Processing interview Questions3

V- Infinite Impulse Response filters

1). What is the order of butter worth filter?

Ans: The order of the butter worth filter is N =

2). The poles of butter worth filter lie on a Circle.

3). The poles of chebyshev filter lie on an ellipse.

4). What is the order of chebyshev filter?

Ans: The order of the chebyshev filter is N =

5). What is the difference between chebyshev type –I and type –II?

Ans: Type –I chebyshev filter are all-pole filters that exhibits equiripple behavior in the pass band and a monotonic characteristics in the stop band. On the other hand, the family of type –II chebyshev filter contains both poles and zeros and exhibits a monotonic behavior in the pass band and an equiripple behavior in the stop band.

6). What is the expression for location of poles of normalized butter worth filter?

Ans: The poles of the butter worth filter is given by

k=1,2,…….,N

7). Distinguish between butter worth and chebyshev (type-I) filter.

Ans: 1). The magnitude response of butter worth filter decreases monotonically as the frequency Ω increases from 0 to

, where as the magnitude response of the chebyshev filter exhibits ripple in the pass band and monotonically decreasing in the stop band.

2). The transition band is more in butter worth filter compared to chebyshev filter.

3). The poles of the butter worth filter lie on a circle where as the poles of the chebyshev filter filter lie on an ellipse.

4).For the same specifications the number of poles in butter worth filter are more when compared to chebyshev filter, i.e., the order of the chebyshev filter is less than that of butter worth filter.

8). How many methods are there to design IIR digital filters from analog filters?

Ans: There are 4 methods. Such as, approximation of derivatives, impulse invariant technique, bilinear transformation and matched z-transform method.

9). What do you understand by back word difference?

Ans: One of the simplest method for converting an analog filter into a digital filter is to approximation the differential equation by an equivalent differential equation

i.e.,

The above equation is known as backward difference equation.

10). What is the mapping procedure between s-plane and z-plane in the method of mapping of differentials?

Ans: The mapping procedure between s-plane and z-plane in the method of mapping of differentials is given by H(z)=

11). What is matched z-transform method?

Ans: It is the method of converting an analog filter into an equivalent digital filter. Suppose that the system function of the analog filter is expressed in the factored form

Where

are the zeros and

are the poles of the filter. Then the system function of the digital filter is

where T is sampling period.

12). What is meant by impulse invariant method of designing IIR filter?

Ans: In this method of digitizing an analog filter, the impulse response of resulting digital filter is a sampled version of the impulse response of the analog filter.

First we express the transfer function of analog filter in partial fraction form, i.e.,

then the transfer function of digital filter can be obtained using the transformation

i.e

., H(z)=

13). What is bilinear transformation?

Ans: The bilinear transformation is

14). What is warping effect?

Ans: The relation between the analog and digital frequencies in bilinear transformation is given by

For small values of w there exist linear relationship between w and

. But for large values of w the relationship is non-linear. This non-linearity introduces distortion in the frequency axis. This is known as warping effect.

15).what are the advantages of bilinear transformation?

Ans: 1. The bilinear transformation provides one-to-one mapping

2. Stable continuous system can be mapped into realizable, stable digital system

3. There is no aliasing.

16). Write the expression for the location zeros of a chebyshev type-II filter?

Ans: The zeros of the chebyshev type-II filter are

k=1,2,…….,N

17). Write the expression for the location poless of a chebyshev type-II filter?

Ans: The poles of the chebyshev type-II filter are

k=1,2,…….N

k=1,…….,N

k=1,……,N

k=1,…..,N ,

k=1,…..,N

18). What is the expression for location of poles of a chebyshev type I filter?

Ans: The poles of the chebyshev filter can be found by using the formula

k=1,2,……..,N

19). If N is odd, the magnitude response of chebyshev type I filter starts at |H(jΩ)|=1.0

20). If N is even, the magnitude response of chebyshev type I filter starts at |H(jΩ)|=

VI – Finite impulse response filters

1). What are the different types of filters based on impulse response?

Ans: Based on impulse response, filters are of two types. Such as IIR filter and FIR filter.

The IIR filters are of recursive type, where by the present output sample depends on the present input, past input samples and output samples.

The FIR filters are of non recursive type where by the present output sample depends on the present input sample and previous input sample.

2). What are the advantages of FIR filters?

Ans:1. FIR filters have exact linear phase.

2. FIR filters are always stable.

3. FIR filters can be realized in both recursive and non recursive structure.

3). Errors due to round off noise are less severe in FIR filters.

4). What are the techniques of designing FIR filters?

Ans: There are two well-known methods for designing FIR filters with linear phase. These are (1) windows method (2) frequency sampling method

5). For what kind of applications, the antisymmetrical impulse response can be used?

Ans: The antisymmetric impulse response can be used to design Hilbert transforms and differentiators.

6). For what kind of applications, the symmetrical impulse response can be used?

Ans: The impulse response, which is symmetrical having odd number of samples can be used to design all types of filters, i.e., LPF, HPF, BPF,BRF

7). What is the reason that FIR filter is always stable?

Ans: FIR filter is always stable because all its poles are at the origin.

8). What condition on the FIR sequence h(n) are to be imposed in order that this filter can be called a linear phase filter?

Ans: The conditions are

(i). symmetric condition h(n)=h(N-1-n)

(ii). Antisymmteric condition h(n)=-h(N-1-n)

9). Under what conditions a finite duration sequence h(n) will yield constant group delay in its frequency response characteristics and not the phase delay?

Ans: If the impulse response is anti symmetrical, satisfying the condition h(n)=-h(N-1-n) the frequency response of FIR filters will have constant group delay and not the phase delay.

10). What are the properties of FIR filters?

Ans: i. FIR filter is always stable.

ii. A realizable filter can always be obtained.

iii. FIR filter has a linear phase response.

11). What is the transfer function of designing FIR filter using fourier series method?

Ans: H(z)=

12).what are the disadvantages of fourier series mehod?

Ans: In designing FIR filter using fourier series method the infinite duration impulse response is truncated at n=

. Direct truncation of the series will response is fixed percentage overshoots and undershoots before and after an approximated discontinuity in the frequency response.

13). What is Gibbs phenomenon?

Ans: Abrupt truncation of the series will lead to oscillation both in pass band and in stop band. This phenomenon is known as Gibbs phenomenon.

14). What is window and why it is necessary?

Ans: One possible way of finding an FIR filter that approximates H(

) would be to truncate the infinite Fourier series at n=

. Abrupt truncation of the series will lead to oscillations in the pass band and stop band. These oscillations can be reduced through the use of less abrupt truncation of the Fourier series. This can be achieved by multiplying the infinite impulse response by a finite weighing sequence w(n), called a window.

15). What is the equation for Hanning window?

Ans: