Voltage Gain Switch (Design Help)

Ken Smith a écrit :

wrote:

Or replace R1 with a cap, which will give a nice dual functions circuit.

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Thanks,
Fred.

I see the 74hc4052 with the enable tied low will guarantee that one of the 4 switches will always be on, so that one of the 4 gains will always be selected, and it handles 2 channels if they both always want the same gain.

There are some seminar notes at Apex which discuss gain switching with relays (pp 26-27 in pdf, seminar pp 34-35}:

They refer to switching the feedback as "bad", but with the hc4052 switch configured so as not to allow open feedback it might be "best".

Glen

The 74HC4052 (at least the version I designed for OnSemi) has a break-before-make circuit built-in... built it's only ~3ns... not many OpAmps will react to that.

I would expect most of the temporary upset to be due to capacitance of the nodes of the feedback network.

Charge injection is ~6pC worst case.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Jim Thompson ha escrito:

Where did you get the 4052's SPICE model ? Or did you make it yourself ? I`ve searched for it in the net high and low, and I can`t find it. PSpice model for 4051 would be great :)

I redesigned ON Semi's whole line of analog switches and a number of the 'HC' and 'LVX' logic parts as well.

So I have ALL the models _at_the_device_level_, i.e. very accurate ;-)

But I can't share :-( NDA's require my silence.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Jim Thompson ha escrito:

I understand.

Still, if anyone could point me in the right direction for a model of this device, I would be grateful :)

[snip]

I don't know if anyone has spun such a model, but you could probably make your own using a voltage controlled switch (Spice VSwitch), an R-C for delay, and a resistor to set the switch on value.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Jim Thompson ha escrito:

Now you can`t throw that off to me like that :), you need to get a little graphical and specific about the analog part. The logic converter and the decoder are easy to do, but I wonder how to stuff all those things inside a single part in PSpice (so I only have to place my

4051, like a normal part), I don`t know even if it is possible. If you could hint how to do it, I`ll search for the rest of the stuff in the help.

Thanks ;)

Read thru the help, a "Part" can actually reference a complete schematic.

The easiest way for novices to make their own part is to copy an existing part, then change attributes (and "Set Schematic") to match your needs.

But you're probably using OrCAD Capture, which is a real bear to use :-(

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.