Fet Buffer for amplifiers

source: http://cappels.org/dproj/edfet/edfet.html

The EDFET drives like a FET, but with the bias stability of bipolar. Amps of output current can be controlled by milliamps of input current. The current gain is a design choice dictated by bandwidth. Two of things you have to consider when adding a power output stage to an op-amp circuit are the frequency response and the cross-over distortion in that stage.

This is especially true with wide band amplifiers, where the unity gain crossover needs to be at several hundred kilohertz. The stage is driven much the same as a complimentary pair output stage, but with the current gain that comes with using FETs., and with feedback within the output stage that that extends the buffer's bandwidth and regulates the quiescent current. More predictable operation allows the designer to design a circuit lower overall power dissipation and better closed loop stability.

The EDFET complimentary buffer is made up of a pair of unity gain buffers, one that drives in the positive direction and the other that drives in the negative direction. Pictured above is the positive driving half of the output stage.

Gain to make the output signal track the input signal comes from inverting transistor, Q1. The input signal is applied to the emitter of Q1 and the output of the amplifier is raised one diode drop to match the forward base-emitter drop of Q1, by diode connected transistor Q2. The buffer's offset is determined by the log of the magnitude of the mismatch in the emitter currents in Q1 and Q2, and it is directly proportional to the absolute temperature.

Since the saturation current usually isn't published for the transistors this expression is only usefully for appreciating the dependence of junction voltage on current and temperature. You can come up with your own value of I0 for a given transistor if you know all the other parameters and solve the above formula for I0. By the way, since, for most practical uses, you will be running at more than a thousand times the saturation current, the "+1" term can be dropped from practical calculations.

As an example, for the audio amplifier using a EDFET buffer shown in Figure 1. The following assumptions are applied: The maximum output voltage is 5 VDC with respect to ground, the power supply (VA) is 12 VDC, the maximum gate voltage is 8 VDC, the input capacitance, Ciss of the BUZ73 is 500 pf, and an...
http://cappels.org/dproj/edfet/edfet.html

Discrete Buffer: Diamond Buffer
Discrete Buffer: JISBOS Buffer

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VHDL code for 1x2 Demultiplexer

library ieee;
use ieee.std_logic_1164.all;

entity bejoy_1x2 is
port(d,s:in std_logic;

z0,z1:out std_logic);
end bejoy_1x2;

architecture arc of bejoy_1x2 is
begin
z0 <= d and (not s);
z1 <= (d and s);
end arc;

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Design Buffers: Improved unity-gain follower delivers fast, stable response

Robert A Pease, National Semiconductor Corp -- EDN, June 27, 2011

Heavy load capacitance can cause the output of a unity-gain follower—an operational amplifier with direct feedback to the inverting input (Fig 1)—to ring and oscillate. The LM110 follower, for example, normally drives a 50-pF load without problems, but it does not drive 500 pF stably—high capacitance significantly modifies the open-loop output impedance, reducing the phase margin to zero and causing oscillation.

You can easily eliminate such instability problems by adding a capacitor and resistor in series across the op amp's inverting and noninverting inputs. This solution can also greatly improve a follower's slew rate.

Analyze the problem

In general, increasing the ac noise gain of an op amp's feedback network improves capacitive-load tolerance. A common gain-increasing strategy adds R₂~R_F/10 to the circuit shown in Fig 2. (A moderate-value capacitor, C₂, usually inserted in series with R₂, prevents the dc noise gain from also increasing and degrading dc-offset, drift and accuracy specifications.)

If the op amp has a 1-MHz gain-bandwidth product and R₁=R_F, the closed-loop frequency response will be 500 kHz. Inserting R₂=R_F/10 drops this frequency response to 90 kHz, where the amplifier usually tolerates a much larger capacitive load. AC noise gain equals (R_F/ R₁)+(R_F/R₂)+1, and dc noise gain is (R_F/R₁)+1.

You can also increase ac noise gain by installing R₃ and C₃ instead of R₂ and C₂. The resulting value is

[1+(R_F/R₁)][(R₊+R₃)/R₃]+(R_F/R₃).

In the simplest case, R₁ forms an open circuit, and ac noise gain equals

(R₊/R₃)+(R_F/R₃)+1.

Therefore, you can raise ac noise gain by using a low value for R₃ and a high value for R₊ and/or R_F.


The solution follows

For the particular case of a unity-gain follower, R_F is normally 0O as shown in Fig 3. According to the foregoing general analysis, if the value of R_S is low, ac noise gain is (R₄/R₅)+1, so you can increase ac noise gain—and therefore stability—by adding a large R₄ and a small R₅. (A large and constant R_S can make R₄ unnecessary; ac noise gain is then (R_S/R₅)+1.)

With LM110/LM310s, for example, 10k is an appropriate value for R₄. Using R₅ = 3.3k and C₅ = 200 pF, the LM110 stably drives capacitive loads up to 600 pF.

Technique speeds followers
You can also wire the resistor/capacitor combination across an op amp's inputs to increase the follower's slew rate. For example, an LF357 op amp's decompensation with a small internal capacitor normally requires gains higher than five to maintain stability (Fig 4). But the LF357 fits unity-gain-follower applications as easily as the LF356 (which is identical to the 357 except for the 356's internal compensation) and achieves better results. When source resistance is less than 1k, both the LF357 and 356 provide fast, stable responses, but the 357 has a 50V/µsec slew rate (typical) compared with 12V/µsec for a 356.

The LM349 decompensated quad op amp furnishes a bipolar input stage with a finite bias current (200 nA max). For best results in this application, add the resistor that controls the noise gain equally to the inverting and noninverting inputs as shown in Fig 5. With this circuit, the LM349 can slew at 2V/µsec typ and handles audio signals much faster—and without distortion—than the compensated LM348 (which, at 0.5V/µsec, slews only as fast as the general-purpose LM741). You can use the same approach for an LM101 by employing a 5-pF damping capacitor.

Watch for problems

While inserting a resistor/capacitor combination across the inputs gives faster slewing, the circuit's bandwidth could degrade if source impedance (R_S) increases. In addition to guarding against bandwidth problems, make sure ac noise doesn't reach an objectionable level when you raise ac noise gain. Although most modern op amps exhibit low noise, raising that noise gain to 10 can significantly increase output noise.

If the series capacitor across the op amp's inputs is larger than necessary for stability and high slew-rate purposes, noise increases unnecessarily. In general, choose the minimum capacitance for the circuit in Fig 3 according to the following formula (where f_V = op amp's unity-gain bandwidth):

C_5min = 4[1+(R₄/R_S)]/2pR₅f_V=(R₄+R₅)/(p/2)f_V(R₅)². To allow for tolerance variations, make C₅'s circuit value two or three times C_5min.

source: http://www.edn.com/article/518641-Improved_unity_gain_follower_delivers_fast_stable_response.php

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VHDL code for Full Subtractor

library ieee;
use ieee.std_logic_1164.all;

entity bejoy_fs is
port(x,y,bi: in bit; b2,do,bo: out bit; d,b: inout bit);
end bejoy_fs;

architecture arc of bejoy_fs is
begin
d<=x xor y;
b<=x and (not y);
do<=bi xor d;
b2<=bi and (not b);
end arc;

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Fake Google powered Antivirus is Malware

Some security researchers have found a fake antivirus which is actually a malware. The strange thing about this malware is that it claims to be powered by Google.

Some highly SEO optimize website with Good ranking in Google Search are being used by attackers to spread this malware. When a user visits any of this malicious website, the website shows a fake virus warning message. This message warns users to download or they will block their access to all Google services. The message says, "Google systems have detected unusual traffic from your computer. Please check your PC on viruses. To continue, please download and install our antivirus software. [DOWNLOAD button] or our system will block your access to Google services."

All those visitors who download the antivirus in order to avoid service blockage of various Google services, served a malware which contains Trojan.Win32.Fakeav.tri (v). This Trojan is really harmful. To know more you can search for this Trojan in Google.  It means a Trojan which is claiming to be a antivirus.

It is my personal suggestion not to believe any of these kinds of spams which claim to be the part of such a big companies. No company launches this company silently. If you are not sure, then search in Google or other search engine to know more before trusting. If you really want to know this kind of new service launched by these companies, follow my other new related website,Techlomedia. This website will update you all the latest service and gadgets launched.

If you have already downloaded this fake antivirus, then scan your whole system to detect and remove this virus. If you have not updated your antivirus for past few days, then update your antivirus because older antivirus will not detect this Trojan signature. You can also download any latest antivirus and internet security suit

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VHDL code for 4 bit Gray to Binary converter

library ieee;
use ieee.std_logic_1164.all;

entity bejoy_g2b is
port(g:in std_logic_vector(3 downto 0);

b:inout std_logic_vector(3 downto 0));
end bejoy_g2b;


architecture a of bejoy_g2b is
begin

b(3)<=g(3);
b(2)<=b(3) xor g(2);
b(1)<=b(2) xor g(1);
b(0)<=b(1) xor g(0);
end a;

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The City of Fools

As a newspaper journalist, you are sent to a small town of Tundel. A UFO is rumored to have landed there, but the local mayor tries to conceal the fact. Geared up to learn the truth about the mysterious event, you try to interview the mayor but finding him appears harder than it seemed. The way to his door turns up a real challenge to your courage, selflessness and wit.
Overcome all the incredible obstacles, find the mayor and become a hero

Download:  Mirror 1 Mirror 2 Mirror 3

 

 

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VHDL code for 4 bit Binary to Gray code converter

library ieee;
use ieee.std_logic_1164.all;

entity bejoy_b2g is
port(b:in std_logic_vector(3 downto 0);

g:out std_logic_vector(3 downto 0));
end bejoy_b2g;

architecture a of bejoy_b2g is
begin

g(3)<=b(3);
g(2)<=b(3) xor b(2);
g(1)<=b(2) xor b(1);
g(0)<=b(1) xor b(0);
end a;

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Windows Xp Genuine Forever 100%

#################################

Windows Xp Genuine Forever

                                  
                                       DOWNLOAD GENUINE FILES


1.Copy all the files from the system32 Folder and 

   paste to  C:WINDOWS:System32/

2.Now go to ///start///---///run///---and type in instexnt install

3.Congratulations,from now u have a genuine copy of Xp

4.U can now add the 1.reg file or restart u pc.

5.Now Run the Microsoft Windows Genuine Check Tool ,

   and see if u PC is 'genuine'. 

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VHDL code for SR Flip Flop

library ieee;
use ieee.std_logic_1164.all;

entity bejoy_rsff is
port(s,r,clk:in std_logic;q,q1,z:inout std_logic);
end bejoy_rsff;

architecture arc of bejoy_rsff is
begin
process(clk)
begin

if clk='1' then
z<=s or ((not r) and q);
q<=z after 5ns;
q1<=not z after 5ns;

end if;
end process;
end arc;

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