Greetings,
The excellent spreadsheet that is provided with AN-912 calculates the 'normal' and 'complementary' impedances on the output of the balanced current-output DAC. For a 1:1 transformer these will be 25 Ohms to give a load impedance of 50 Ohms. However, if two 50 Ohms resistors are used on the DAC output (as is the case in the evaluation board) there is an increase in power of almost 2.5 dB. Is there a downside? What is the effect on the signal purity with this configuration where Zs is not equal to RL? Is there a limit? I am using the 2nd Nyquist zone and have to boost a broadband sweep (500 to 700 MHz) to compenaste for the sinc doop. By using two Ik Ohm resistors the output is increased by ~ 5.8dB and I can use cheaper amplifiers. Having an impedance mismatch goes against the grain and I don't have the tools to design a bandpass reconstruction filter with differing input and output impedances. Thank you