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In this circuit LM358N 1MHz 32V dual op amp is used (+12V and -12V). The question is, can I simply replace it with NE5532N 10MHz +-22V dual op amp for up to 8MHz DDS signal source?

Basically, this circuit has DDS output generated via R2R resistor network and adjusted via LM358N offset and amplitude regulating circuits. Offset can be regulated in range +5V..-5V while amplitude in range 0..10V.

DUAL OP AMP LM358N

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Given that you won't be able to get much more than a 250 kHz sine wave with a software DDS running on an AVR, it doesn't matter much what op amp you use.

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  • \$\begingroup\$ 3 cycles for SRAM byte read from postincremented X is enough for 8MHz PORT output (4MHz on/off) if AVR is clocked at 24MHz (XMEGA can go up to 32MHz), and instructions are ordered one after another without any jump (but for the last read from the table in SRAM). Of course, such frequencies are off the limit for more complex signal shapes, but I was pointing 8MHz as a safe margin. \$\endgroup\$ – avra Apr 4 '11 at 22:24
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    \$\begingroup\$ Have you actually achieved an 8 MHz output? If it's a square wave you will need a much higher performance op amp than a 10 MHz one. \$\endgroup\$ – Leon Heller Apr 4 '11 at 22:44
  • \$\begingroup\$ Thank you for this valuable input. So far I have verified simple 3 cycles code in simulator, so I think it is doable (actually even 30% better then that if 32MHz is used instead of 24MHz). I don't know yet how the signal will look on oscilloscope. The only faster opamp I can get is LM318N08 (single 15MHz). Should I bother, or should I just redirect those high frequency squares directly to the output without opamp? Can you guess then if opamp could handle my table based DDS signals properly at least up to about 1MHz? \$\endgroup\$ – avra Apr 5 '11 at 6:34

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