DDS Post Amplifier

The DDS post amplifier is an important and tricky circuit. It needs the following characteristics:

• Flat out to about 50 Mhz
• Good high impedance input so as to not “double load” the already terminated DDS module output filter.
• About 14 dB gain
• Powered from USB 5VDC

I’ll be writing about this block in detail, but for now, here’s the schematic and measured frequency response plot of the prototype:

  

You can see that the gain is within +/- 1 db of 14 dB from less than 1 Mhz to 50 Mhz. Output level is almost uncompressed up to +10 dBm. Input impedance is greater than 1000 ohms over most of the range; output return loss is around -17dB,  but there’s room for further improvement.

 

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