# 0.5 Sampling with automatic gain control  (Page 15/19)

 Page 15 / 19

There are two basic approaches to an AGC. The traditional approach uses analog circuitry to adjust the gain before the sampling. The more modern approach uses the output of the sampler to adjust thegain. The advantage of the analog method is that the two blocks (the gain and the sampling) are separate and do not interact.The advantage of the digital adjustment is that less additional hardware is required since the DSP processing is already presentfor other tasks.

A simple digital system for AGC gain adjustment is shown in [link] . The input $r\left(t\right)$ is multiplied by the gain $a$ to give the normalized signal $s\left(t\right)$ . This is then sampled to give the output $s\left[k\right]$ . The assessment block measures $s\left[k\right]$ and determines whether $a$ must be increased or decreased.

The goal is to choose $a$ so that the power (or average energy) of $s\left(t\right)$ is approximately equal to some specified ${\mathbf{s}}^{2}$ . Since

${a}^{2}{\left(\text{avg},\left\{,{r}^{2},\left(t\right),\right\}|}_{t=kT}\approx \text{avg}\left\{{s}^{2}\left(kT\right)\right\}\approx \text{avg}\left\{{s}^{2}\left[k\right]\right\},$

it would be ideal to choose

${a}^{2}\approx \frac{{\mathbf{s}}^{2}}{\text{avg}\left\{{r}^{2}\left(kT\right)\right\}},$

because this would imply that $\text{avg}\left\{{s}^{2}\left(kT\right)\right\}\approx {\mathbf{s}}^{2}$ . The averaging operation (in this case a movingaverage over a block of data of size $N$ ) is defined by

$\text{avg}\left\{x\left[k\right]\right\}=\frac{1}{N}\sum _{i=k-N+1}^{k}x\left[i\right]$

Unfortunately, neither the analog input $r\left(t\right)$ nor its power are directly available to the assessment blockin the DSP portion of the receiver, so it is not possible to directly implement [link] .

Is there an adaptive element that can accomplish this task? As suggested in the beginning of "Iteration and Optimization" , there are three steps to the creation of a viableoptimization approach: setting a goal, choosing a solution method, and testing. As in any real life engineering task, a propermathematical statement of the goal can be tricky, and this section proposes two (slightly different) possibilitiesfor the AGC. By comparing the resulting algorithms (essentially, alternativeforms for the AGC design), it may be possible to trade off among various design considerations.

One sensible goal is to try to minimize a simple function of the difference between the power of the sampled signal $s\left[k\right]$ and the desired power ${\mathbf{s}}^{2}$ . For instance, the averaged squared error in the powers of $s$ and $\mathbf{s}$ ,

$\begin{array}{cc}\hfill {J}_{LS}\left(a\right)& =\text{avg}\left\{\frac{1}{4},{\left({s}^{2}\left[k\right]-{\mathbf{s}}^{2}\right)}^{2}\right\}\hfill \\ & =\frac{1}{4}\text{avg}\left\{{\left({a}^{2}{r}^{2}\left(kT\right)-{\mathbf{s}}^{2}\right)}^{2}\right\},\hfill \end{array}$

penalizes values of $a$ which cause ${s}^{2}\left[k\right]$ to deviate from ${\mathbf{s}}^{2}$ . This formally mimics the parabolic form of the objective [link] in the polynomial minimization example of the previous section.Applying the steepest descent strategy yields

$a\left[k+1\right]=a\left[k\right]-\mu {\left(\frac{d{J}_{LS}\left(a\right)}{da}|}_{a=a\left[k\right]},$

which is the same as [link] , except that the name of the parameter has changed from $x$ to $a$ . To find the exact form of [link] requires the derivative of ${J}_{LS}\left(a\right)$ with respect to the unknown parameter $a$ . This can be approximated by swapping the derivative and the averaging operations to give

$\begin{array}{c}\\ \hfill \frac{d{J}_{LS}\left(a\right)}{da}& =& \frac{1}{4}\frac{d\text{avg}\left\{{\left({a}^{2}{r}^{2}\left(kT\right)-{\mathbf{s}}^{2}\right)}^{2}\right\}}{da}\hfill \\ & \approx & \frac{1}{4}\text{avg}\left\{\frac{d{\left({a}^{2}{r}^{2}\left(kT\right)-{\mathbf{s}}^{2}\right)}^{2}}{da}\right\}\hfill \\ & =& \text{avg}\left\{\left({a}^{2}{r}^{2}\left(kT\right)-{\mathbf{s}}^{2}\right)a{r}^{2}\left(kT\right)\right\}.\hfill \end{array}$

find the 15th term of the geometric sequince whose first is 18 and last term of 387
The given of f(x=x-2. then what is the value of this f(3) 5f(x+1)
hmm well what is the answer
Abhi
how do they get the third part x = (32)5/4
can someone help me with some logarithmic and exponential equations.
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
I don't understand what the A with approx sign and the boxed x mean
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
oops. ignore that.
so you not have an equal sign anywhere in the original equation?
hmm
Abhi
is it a question of log
Abhi
🤔.
Abhi
Commplementary angles
hello
Sherica
im all ears I need to learn
Sherica
right! what he said ⤴⤴⤴
Tamia
hii
Uday
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
a perfect square v²+2v+_
kkk nice
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
rolling four fair dice and getting an even number an all four dice
Kristine 2*2*2=8
Differences Between Laspeyres and Paasche Indices
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
how do you translate this in Algebraic Expressions
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
types of nano material
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
what is nano technology
what is system testing?
preparation of nanomaterial
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
what is system testing
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
how did you get the value of 2000N.What calculations are needed to arrive at it
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!