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High-precision digitally controlled amplifier

Question asked by Sparkles! on Jul 6, 2014
Latest reply on Jul 14, 2014 by Sparkles!

Hi everyone,



I am trying to build a high-precision digitally controlled amplifier in order to amplify signals coming out from AD9833. I would like to precisely amplify that output signal from around 1Vpp to 12Vpp in steps of 10mV or 20mV. AD9833 uses a 25MHz MCLK, thus the highest frequency expected is to be around 12.5MHz. However, square and triangular waves need much higher bandwidth so as not to destroy their high frequency components.


I have already been searching a voltage controlled amplifier in Variable Gain Amplifiers (VGA) | Specialty Amplifiers | Analog Devices comprehensively, but I cannot find anything that suits: I would need a wide bandwidth, linear-in-voltage, high-precision VGA (no PGA with a few fixed values). All those VGAs seem to be video signal or line-driving oriented and do not offer me a simple interface to control. I just would need a DC control pin or a serial SPI interface.


I have also thought of using an instrumentation amplifier Instrumentation Amplifiers | Analog Devices together with a digital potentiometer Digital Potentiometers | D/A Converters | Analog Devices placed as Rg to control the gain. Digital pots have low bandwidth so I cannot use them in the amplification network nor even as an attenuator, but since in this sort of amplifiers they only balance the inner current to modulate the gain perhaps will work. What do you think?



Could someone give me some advice about what to choose or the best form to achieve this challenging amplification?

Thank you for your time