The ADT1-1WT transformer is used in the evaluation of ad9910 dds IC. The transformer is used to improve the gain. So can the required frequency can be obtained at the filter output without using adt1-1wt transformer ?
The transformer serves a number of functions:
The only major disadvantage is that the transformer limits low frequency performance.
Although bypassing the transformer is possible, it generally comes at the cost of reduced spectral performance.
Why do you want to bypass the transformer?
Problem is unavailability of the transformer in short time.
Is there any alternative for the transformer?
We have used the AD9910 with the WBC1-1TL transformer from Coilcraft. You can order it directly from their website, they have it in stock.
There may be a direct replacement available from another source (I've never checked). You basically need a center tapped transformer, preferably 50-ohm, with a 1:1 turns ratio and sufficient bandwidth for your application.
Can the transformer be replaced with a circuit of inductors resistors capactos?
I am working at 400Mhz frequency.
With enough time and resources, I suppose one could design a circuit that emulates a transformer, but you would be on your own for such an undertaking.
Although the transformer simplifies the interface to the DAC's balanced output and tends to yield the best overall performance, it is not an absolute requirement. With some care, you should be able to design a circuit to convert the DAC's current output to a useable voltage signal. However, you must adhere to the constraint of DAC's output compliance range (+/- 0.5V), which severely limits your options. You can even use an differential op-amp circuit at the output, but finding one with the necessary bandwidth is problematic.
Furthermore, designing a reconstruction filter with the appropriate impedance transformation may be a challenge. You need to design the filter to match the impedance of your final output load to the impedance of whatever DAC output network you come up with. This alone is a compelling reason to use a transformer.
Note you can get an output signal from the DAC by connecting a resistor (typically in the neighborhood of 25 ohms) from one of the DAC output pins to GND. However, with a simple resistive load, you will be dealing with a DC offset. If you intend to connect other loads to the DAC output, the DC offset is a consideration.
Filtering the signal is another story. However, if signal purity is not a defining requirement, then you can get away with no filter at all.
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