Question

Block diagram of a real time signal processing system is shown in Figure 1. Assuming that the system operates in audio frequency band (0 to 20 KHz) and uses bipolar, analog to digital converter (ADC) with peak to peak input voltage range= 10 Volt is used, estimate: i. The quantization step size; (2 Marks) ii. The minimum stop band attenuation in dB, Amin, for the anti-aliasing filter; (4 Marks) iii. Sketch the frequency response of the antialiasing filter; iv. The level of the aliasing error relative to the signal level in the pass band for the estimated Amin and minimum sampling frequency Fs to maintain the aliasing error within specified limit. v. Comment on the system if the input filter is changed to fourth order

Answer 1

Solution:- In ADC Converter a) The quantization Step size (A) = Peak to Peak voltage 2-1 where n = number of bits Here n=10 A I- 10 : 0.00977 1023 210.1 1024-1 b) The minimum Stop band attenuation in dB, Amin, for the anti- aliasing filter aullio freq band = - 20KHZ te = 2fm - 40 KHZ => felfm > 2 1010g lie => 10l0g (a) - Anun 0.301X 10 dB | Arun - 3:01 dB e) frequency response of the antfaliasing filter Filter o/p Filter LP transition bond ti fregrany fi fa Preck (Ideal) (Practical) (d) Minimum sampling frequency fiz, afm fo > 4x20 => faran = 40 KHZ

then e) If filter is changed to fourth order, transition band Sharpness of will increase olpa fi f fe frequency