Signal Processing Stack Exchange
Signal Processing Stack Exchange

Questions tagged [fixed-point]

89 questions
10
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5 answers

Relative merits of fixed point vs floating point computation?

I have a digital signal processing system that operates on a fast x86 machine using double precision floating point numbers. It occurred to me that I am not really using the huge dynamic range of the floating point representation -- all quantities…
nibot
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1 answer

Fixed point multiplication with negative numbers

I am stumped on a simple problem. Let's say I have two 4 bit numbers in Q0.3 format. One sign bit and three fractional bits. So I can represent $-1$ through to $0.875$. Let's now say I wish to do this calculation: $-0.25 \times 0.875$. Which…
benjwy
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1 answer

Converting ADC output to fixed-point format

I want to convert the two's complement, 16-bit output from an ADC into a generic fixed-point format, $\rm Qm.n$, where $\rm m$ is the number of integer bits and $\rm n$ is the number of fraction bits. Any hints/procedure to do this job would be…
Subba Rao
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1 answer

Multiplication of fixed-point numbers

I'm trying to understand the professor who wrote about Q2-fixed-point number 1.01 and 1.11 which should be multiplied. I don't understand anything. Multiply the Q2-fixed-point number 1.01 and 1.11 and give the result as a Q4-number. Answer: 1.01…
Niklas Rosencrantz
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2
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How do I calculate the range of a fixed-point number with $a$ integer bits and $b $ fractional bits?

What does fixed-point number range represents? Why we use formula $2^a - 2^{-b}$, why minus $2^{-b}$? Where $a$ is number of integer bits, and $b$ is number of fractional bits. If we have for example $a = 8$ and $b = 2$, don't we have a possibility…
user20705
1
vote
2 answers

Fixed point restrictions with respect to DSP

I assume that fixed-point arithmetic can handle most of the traditional linear DSP tasks. As far as I know, there is a restriction for the FFT length with respect to the fixed point bit-depth. Is there any common knowledge regarding other DSP…
Gideon Genadi Kogan
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Word-length optimization of a fixed point chain of multipliers

Let's suppose a chain of 6 multipliers: $b = a_1*a_2*a_3*a_4*a_5*a_6*a_7$, where $b$ is the output, and $a_i$ the inputs with 16 bits. How can I optimize the word lengths of the output of each multiplier in order to minimize the fixed point error…
eduardocreta
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1 answer

Fixed point saturation and round

Another question related to fixed point saturation and rounding. Say using notation S where S means it is signed number, WL is the full bitwidth, and FW is the fractional bitwidth. So S<16, 15> means a 16-bit signed number that has 15-bit…
hbf
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0
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1 answer

Calculate error introduced into DSP algorithm

Lets take an algorithm as an example, the DCT-II used in JPEG. The formula is as follows: Now the thing is that, the values in M are not integers and many are even less than 1. We have two options: 1) Fixed point maths and 2) Floating point maths.…
quantum231
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$\rm Q$ number format singed or unsigned?

I am studying $\rm Q$ number formats and in a few places it's used to represent $2$'s complement fixed point numbers , and other places it's used to represent unsigned fixed point numbers. Given a $\rm Q$ number e.g $\rm Q1.4$: How do I know if…
BubbleBoy
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Fixed Point queries-1

I would really appreciate if I can get answers to following Fixed point queries(part-1): Converting a real number x to fixed point fraction X(m,n) [1] says: m = ceil(log2(max[abs(xmin,xmax)+1])) { assuming signed x>1) or m =…
user915783
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1 answer

What is the correct way to handle Saturation on a DSP?

Let's say I have 16 bit fixed point DSP, and am performing a multiply accumulate operation in a loop- What would be the correct way to check for saturation of the accumulated value? As far as I understand, replacing the exceeded value with the…
Naveen
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2 answers

Fixed point conversions

Have following questions about Fixed point conversion format. Suppose I want to change Fixed Point format as X1(m1,n1) (→) X2(m2,n2),m1+n1=m2+n2[Word length same], n2>n1[ Higher Fractionlength] Suppose X1=00001100 and suppose I do X1<<(2^3) …
user915783
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