any idea for this problem?


> ---------- Forwarded message ----------
> Date: Mon, 24 May 1999 12:27:48 +0700 (GMT+0700)
> From: Tan Sing <tsl@stones.com>
> To: Lauw Lim Un Tung <tung@peter.petra.ac.id>
> Subject: Re: Sample & Hold Circuit (fwd)
>
>     Have you checked if the impedance of your multimeter is not affecting
> the circuit ?
>
>     Try to buffer the output with a voltage follower.
>
> Best regards,
> Alexandre Guimaraes
> alexg@iis.com.br
>
> -----Mensagem original-----
> De: Tan Sing <tan-sing@CHEERFUL.COM>
> Para: Multiple recipients of list EDESIGN <EDESIGN@mercury.cc.uottawa.ca>
> Data: Domingo, 23 de Maio de 1999 06:26
> Assunto: Sample & Hold Circuit
>
> >Dear Netters,
> >I am using LF398 (DIP8) for my sample & hold circuit. In the datasheet, it
> >is mentioned that the output voltage in hold mode will remain quite a long
> >time. Unfortunately when I used it in my circuit, the output voltage drops
> >very quickly in hold mode. I tried to change the capacitor from 1 nF, 10nF,
> >100nF, 1uF, 10uF to 100uF. from ceramic type, electrolytic, to tantalum
> >capacitor. But the symptoms remains the same. I tried to change several
> >ICs, but the result were also the same. In the datasheet, it says that
> >using 1 uF will have the output voltage drop of 5 mV/min. But This doesn't
> >happen in my circuit. I just used the typical application of LF398, and
> >directly measure the output voltage using a digital multimeter.
> >I wonder what could possibly be the cause of this symptoms ??? Because the
> >circuit application just consists of 1 IC and 1 cap. I have replace them
> >with some capacitor and some ICs, but it seems it doesn't help.
> >I used Philips Semiconductor DIP8 LF398, and also National Semiconductor
> >DIP8 and Metal Can Package LF398. The result was the same.
> >
> >Is there anybody who could give me any suggestions ???
> >
> >Thank you.
> >