[quote=hk大飛]好像不是的。n2pk好像是用zif+adc的。[/quote]
大飞说的对
most lab-quality vnas use a superhet architecture that converts both the reference signal and the detected signal to a fixed if for precision amplitude and phase detection. these conversions occur via conventional mixing or sampling. this architecture, as normally implemented, is complex and expensive. a much simpler architecture is used in the recent 'vna on a chip' device - the analog devices ad8302, with its broadband logarithmic detection of amplitude information and high-speed logic for the phase comparison. the disadvantage here is considerably reduced accuracy compared to a lab-quality vna.
this vna is different - it uses a narrow-band direct-conversion architecture that is much simpler than superhet vnas, but is also much more accurate than the log-detection devices. because the detector in this vna converts down to dc, the only output available is a dc voltage, which is dependent not only on the magnitude of the rf voltage at its input, but also its phase relative to the rf signal at its lo input. highly accurate measurements of this amplitude and phase dependent dc voltage are obtained using a precision linear analog detector, a 24-bit analog-digital converter (adc), and precise phase control of the lo dds.
