Hi all,

I am designing a simple sample and hold circuit where the input is a sinusoidal analog input and it is control by a TTL compatible square wave (waveform A). The result waveform i should get is waveform B in the attach file but i tried a millions time i still cant get the same waveform. Someone there can help me out? I had attached all the file in the attachment..

 

Hi all,

I am designing a simple sample and hold circuit where the input is a sinusoidal analog input and it is control by a TTL compatible square wave (waveform A). The result waveform i should get is waveform B in the attach file but i tried a millions time i still cant get the same waveform. Someone there can help me out? I had attached all the file in the attachment..

I can make a sample and hold (track and hold, more accurately) using your circuit, with a couple of mods. On mine, though, when the sample pulse goes high, the output follows the input instead of being clipped at ground like your output waveform.

 

Can you get the same result as the waveform in 'B' using the circuit i constructed?

 

If you want a sample and hold circuit, you can try using the HA-5320 IC. It is a sample and hold circuit IC. I have already used it and it is working...Below is the link to its datasheet:

http://www.intersil.com/data/fn/fn2857.pdf

 

Can you get the same result as the waveform in 'B' using the circuit i constructed?

Below is my circuit and the results. I have included the .ASC file so that it can be simulated in LTspice.
I used a different op amp because I did not have a model of LF412.

 

Ron..

Your result is exactly what i want..anyway i cant open the file you attached here..can you send me the LF356.sub? Thank you =)

 

Copy and paste this into Notepad, and save it as ...\lib\sub\LF356.sub.

* connections:    non-inverting input
*                 |   inverting input
*                 |   |   positive power supply
*                 |   |   |   negative power supply
*                 |   |   |   |   output
*                 |   |   |   |   |
*                 |   |   |   |   |
.SUBCKT LF356     1   2  99  50  28
*
*Features:
*Low input bias current =             30pA
*Low input offset current =            3pA
*High input impedance =              1Tohm
*Low input offset voltage =            1mV
*
****************INPUT STAGE************** 
*
IOS 2 1 3P
*^Input offset current
R1 1 3 1E12
R2 3 2 1E12
I1 99 4 100U
J1 5 2 4 JX
J2 6 7 4 JX
R3 5 50 20K
R4 6 50 20K
*Fp2=20 MHz
C4 5 6 1.9894E-13
*
***********COMMON MODE EFFECT***********
*
I2 99 50 4.65MA
*^Quiescent supply current
EOS 7 1 POLY(1) 16 49 3E-3 1
*Input offset voltage.^
R8 99 49 50K
R9 49 50 50K
*
*********OUTPUT VOLTAGE LIMITING********
V2 99 8 2.63
D1 9 8 DX
D2 10 9 DX
V3 10 50 2.63
*
**************SECOND STAGE**************
*
EH 99 98 99 49 1
F1 9 98 POLY(1) VA3 0 0 0 1.5944E7
G1 98 9 5 6 2E-3
R5 98 9 100MEG
VA3 9 11 0
*Fp1=31.96 HZ
C3 98 11 49.9798P
*
*********COMMON-MODE ZERO STAGE*********
*
G4 98 16 3 49 1E-8
L2 98 17 530.52M
R13 17 16 1K
*
**************OUTPUT STAGE**************
*
F6  99 50 VA7 1
F5  99 23 VA8 1
D5  21 23 DX
VA7 99 21 0
D6  23 99 DX
E1  99 26 99 9 1
VA8 26 27 0
R16 27 28 20
V5  28 25 -.25V
D4  25  9 DX
V4  24 28 -.25V
D3   9 24 DX
*
***************MODELS USED**************
*
.MODEL DX D(IS=1E-15)
.MODEL JX PJF(BETA=1.25E-5 VTO=-2.00 IS=30E-12)
*
.ENDS

 

Ron..

Thanks ron..actually i am using Labcenter Proteus to do my simulation..but i already tried to use LTspice and it works.. but i wonder what parameter you change to get the sample waveform? I only can get the hold waveform with my Proteus.. so i need to know which parameter i can change to get sample waveform.. the switch is not the active device rite?

 

Thanks for your help =)

 

Ron..

Thanks ron..actually i am using Labcenter Proteus to do my simulation..but i already tried to use LTspice and it works.. but i wonder what parameter you change to get the sample waveform? I only can get the hold waveform with my Proteus.. so i need to know which parameter i can change to get sample waveform.. the switch is not the active device rite?

I'm not familiar with Proteus. Maybe one of the other members can help.

 

Ron,

Now i have a similar question about it. What if i change the input voltage source to a input current source?the result waveform i want to get is exactly the same with the previous input voltage source. I tried to replace the input voltage source already but i still cannot get the correct output sample and hold waveform. The output waveform of the current i get is continuous zero value. So do you have any idea? Please reply me asap if possible. Thank you

 

Why do you want to use current as an input? Where is the current coming from?
Current will not flow into an open circuit (the input of U1). Remember Ohms law: V=I*R. If R is infinite, V will be infinite.

 

Your sample and hold circuit needs a voltage input to work. To convert a current source back to a voltage, put a resistor of a suitable value from the U1 + input to ground.

Regards,
Ifixit

 

Your sample and hold circuit needs a voltage input to work. To convert a current source back to a voltage, put a resistor of a suitable value from the U1 + input to ground.

Regards,
Ifixit

Or dump it into the inverting input of a feedback amplifier.

 

Based on the journal, there's 2 sample/hold circuit. One for input voltage signal and another one for input current signal? So i need to construct a sample/hold circuit with current input...