B. P. Lathi, Zhi Ding - Modern Digital and Analog Communication Systems-Oxford University Press (2009)

314 SAMPLING AND ANALOG-TO-DIGITAL CONVERSION
Figure 6.4 1
Reconstructed
signal spectrum
and waveform
from applying
the simple
rectangular
reconstruction
pulse (Fig. 6.6)
followed by LPF
without
equalization.
0
-1
Original signal versus flat-top reconstruction
0.1 0.2
0.3 0.4 0.5
Time, second
0.6 0.7
0.8 0.9
Original and flat-top reconstruction after LPF
2,----"-"T"----,---...c,-----,-----,----.----.----"-"T"----,-----;1
--- Original signal
LPF reconstruction
0
-I
'I
'I
V
-2 '----'-----.L----'------'-----'-----'-----'-""""-=-'----.L----'
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Time, second
q_l evel=sig_nmax+Delta/2 :Delta:sig__pmax-Delta/2 ; % de fine Q-levels
L_sig=length (sig_in) ; % find signal length
sigp= (sig_in-sig_nmax) /Delta+l/2; % convert into 1/2 to L+l/2 range
qindex=round (sigp) ; % round to 1, 2, ... L levels
qindex=min ( qindex,L) ; % eleminate L+l as a rare possibility
q_out=q_level (qindex) ; % use index vector to generate output
SQNR=20*log10 (norm(sig_in)/norm (sig_in-q_out )); %actual SQNR value
end
The function sampandquant .m executes both sampling and uniform quantization
simultaneously. The sampling period ts is needed, along with the number L of quantization
levels, to generate the sampled output s_ou t, the sampled and quantized output sq_ou t,
and the signal after sampling, quantizing, and zero-order-hold sqh_out.
% (sampandquant .m)
function [s_out ,sq_out, sqh_out,Delta, SQNR] = sampandquant (sig_in, L, td, ts)
% Usage
% [s_out , sq_out,sqh_out ,Delta, SQNR] =sampandquant (sig_in,L, td, fs)
% L number of uni form quantization levels
% sig_in - input signal vector
% td original signal sampling period of sig_in