gain control for 100Mhz

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hi
i build a function gen that its output frequency is about 100 MHz
i want the amplitude of wave be variable
maybe i use gain control but its expensive
i want something cheap.
anybody know a way?

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navidrct wrote:

i build a function gen that its output frequency is about 100 MHz
...

You are building

or

You have built

?

Please let us know what are you saying correctly.

navidrct wrote:

...
i want the amplitude of wave be variable
maybe i use gain control but its expensive
...

Why don't you show us your circuit?

navidrct wrote:

...
i want something cheap.
anybody know a way?

If I were you, I would put something about my circuit and mention everything about what I expected to get from the output of my circuit.

What have you done so far?

e.g. have you searched in the site of some distributors?(to find any specific components) like Mouser,Digikey,...

"One's value is inherent; money is not inherent"

 

Chuck, you are in my heart!

Last Edited: Mon. Oct 12, 2015 - 08:02 AM
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Ua1496?
Theres a number of devices with a 'gilbert cell'. Use Google.
You might be able to use a varicap diode. So many ways..........

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Kartman wrote:

Ua1496?
Theres a number of devices with a 'gilbert cell'. Use Google.
You might be able to use a varicap diode. So many ways..........

thanks ill look in to that

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Kartman wrote:

Ua1496?
Theres a number of devices with a 'gilbert cell'. Use Google.
You might be able to use a varicap diode. So many ways..........

 

i simulate it in ltspice

help me to understand

 

Attachment(s): 

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I Have a DAC that its full range output is 30mA

iim using this circuit and turn it to -5 and 5 v

my output DAC circuit

 

now i want this 5 and -5 to be variable by user

i want to use gain controller but its so expensive

i want know how can i do that cheaper

my freq is 100MHz

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You want a digital step attenuator. Something like this.

 

Greg

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Why not vary the DAC reference voltage? 

 

Also check Analog Devices. They have many RF building blocks. Not cheeeeeep, but reasonable for what they do. Most are good to 500MHz or so.

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Decide upon the output levels that you want.  Use a pair of resistors as a divider for each level.   Use a 100+MHz bandwidth transistor to buffer each output level.  

 

Or, search Digikey.com as central library resource of electronic parts to find 100+MHz op amps.

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You assume i know how a gilbert cell works - sorry i cant help. I'd be using Google to answer that question.

Your simulation is not at 100MHz, so what is the use of this? 100pF is a virtual short at those frequencies. I think you need to give us more information on what is the dac and what range and precision you want. Realise that the question you are asking is not trivial. Parasitic inductance and capacitance makes it a challenge to implement. What looks like a resistor at 1kHz is somewhat different at 100MHz.

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AD827 will NEVER do 100MHz. Its unity gain frequency is only 50MHz. Plus, the component values make little sense for those frequencies. For that matter, the whole idea of an op-amp at 100MHz is neither easy nor low-cost.

 

What DAC are you using? You will need to update the output at probably 1GHZ to get anything that even looks halfway like a 100MHz sine. Even that will have lots of distortion. Or, are you talking about a 100MHz sample (update) rate? If so, your simulation is highly unrealistic.

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

Last Edited: Tue. Oct 13, 2015 - 01:26 AM