constraincoeffwl
Constrain coefficient word length
Syntax
Hq = constraincoeffwl(Hd,wordlength)
Hq = constraincoeffwl(Hd,wordlength,'Ntrials',N)
Hq = constraincoeffwl(Hd,wordlength,...,'NoiseShaping',NSFlag)
Hq = constraincoeffwl(Hd,wordlength,...,'Apasstol',Apasstol)
Hq = constraincoeffwl(Hd,wordlength,...,'Astoptol',Astoptol)
Description
Hq = constraincoeffwl(Hd,wordlength) returns a fixed-point filter
Hq meeting the design specifications of the single-stage or
multistage FIR filter object Hd with a wordlength of at most
wordlength bits. For multistage filters,
wordlength can either be a scalar or vector. If
wordlength is a scalar, the same word length is used for all
stages. If wordlength is a vector, each stage uses the corresponding
element in the vector. The vector length must equal the number of stages.
Hd must be generated using fdesign and
design. constraincoeffwl uses a stochastic
noise-shaping procedure by default to minimize the wordlength. To obtain repeatable
results on successive function calls, initialize the uniform random number generator
rand
Hq = constraincoeffwl(Hd,wordlength,'Ntrials',N) specifies
the number of Monte Carlo trials to use. Hq is
first filter among the trials to meet the specifications in Hd with
a wordlength of at most wordlength.
Hq = constraincoeffwl(Hd,wordlength,...,'NoiseShaping',NSFlag) enables or
disables the stochastic noise-shaping procedure in the constraint of the word length. By
default NSFlag is true. Setting
NSFlag to false constrains the word length
without using noise-shaping.
Hq = constraincoeffwl(Hd,wordlength,...,'Apasstol',Apasstol) specifies
the passband ripple tolerance in dB. 'Apasstol' defaults
to 1e-4.
Hq = constraincoeffwl(Hd,wordlength,...,'Astoptol',Astoptol) specifies
the stopband tolerance in dB. 'Astoptol' defaults
to 1e-2
You must have the Fixed-Point Designer™ software installed to use this function.
Examples
Design fixed-point filter with a word length of at most 11 bits using constraincoeffwl.
Hf = fdesign.lowpass('Fp,Fst,Ap,Ast',.4,.5,1,60); Hd = design(Hf,'equiripple'); % 43 coefficients Hq = constraincoeffwl(Hd,11); % 45 11-bit coefficients [HHd,Wd] = freqz(Hd); HHq = freqz(Hq); plot(Wd/pi,[db(HHd) db(HHq)]) legend("Floating-point Filter","Fixed-point Filter")
Version History
Introduced in R2011a
