What minimum ADC BW i should have for HMC760?
What about HMCAD1520?
What about AD7357?
Can you give more information about your application?
What is the bandwidth of the signal you want to sample?
From DC to 5 GHz.
HMCAD can support 160MPSP to 1000MSPS. You can sample signals with instantenous bandwidth smaller than 500MHz with 8bit resolution or smaller bandwidth signals with higher bit precision.
As i know HMCAD1520 has 700 MHz BW at 500 MPSP 12 bit and 650 MHz BW at 1000 MPSP 8 bit. So if i have 5 GHz track and hold amplifier before ADC do i can make sampling up to 5 GHz signal at equivalent sampling time?
At other side. what BW is at 0.1 dB for 500 MPSP and 1000 MPSP?
Although several high speed ADCs offer enhanced sample rates, few of them offer input bandwidth beyond a few GHz. In addition, maintenance of good sampling linearity at frequencies above the UHF band is technologically challenging and most current ADCs suffer rapidly degrading linearity above 1 or 2 GHz signal frequency. These limitations result from the Track-and-Hold Amplifier inside ADCs which sample the input signal at a precise time instant and holds the value of the sample constant during the analog-to-digital conversion. This THA is often not optimized for ultra wideband operation.
These limitations can be overcome by using external wideband Track-and-Hold Amplifier, which is designed for use in microwave data conversion applications requiring maximum sampling rate, low noise and high linearity over a wide bandwidth. They are used as an external master sampler at the front end of an ADC. Once extended bandwidth sampling takes place within the HMC760, the low bandwidth held output waveform can be processed by an ADC with substantially reduced bandwidth. ADC converter linearity limitations at high input frequencies are also mitigated because the settled THA waveform is processed with the optimal low frequency linearity of the ADC.
The result is an extension in input bandwidth, substantial improvement in high frequency linearity and improved high frequency S/N ratio for the THA-ADC assembly compared to the performance of the ADC alone.
Regarding your question, with HMC760 and HMCAD1520 paired, you can sample signals up to 5GHz, with 1000/640/105 MSPS specified by your ADC using correct anti-aliasing filter.
Thank you for your answer.
But I am still have a problem. When i'm sampling at equivalent random time, cant get good rise time from ADC. At HMC760 input i have fast rise time square signal less then 100ps 10%-90%. At ADC output i never cant get what have at HMC760 input . What acquisition time is for ADC internal THA? Between HMC760 and HMCAD1520 i use diff amp ADL5565.
What is the preamplifier-2 you are using?
Pre-Amp 2 is ADL5565 at gain 6dB.
ADL5565 at 6dB gain has an input impedance of 200ohms(dfferential). The output impedance of HMC760 is 100ohms(differential). There is an impedance mismatch here. for 12dB gain of ADL5565, input impedance is 100ohms. Can you try your setup with this configuration as well?
I put at each ADL5565 input 100 0hms to ground to make 100 ohms diff input.
Can you try to bypass ADL5556 and directly connect HMC760 and HMC1520?
can you please send waveforms that you mentioned at the output of the HMCAD1520 and at the output of HMC760 please?
The large signal rise time of the ADL5565 is close to 1 ns (@ 15.5 dB, datasheet Fig. 23, faster for 6 dB and smaller signal), so that is probably what limits signal rise time at the ADC.
It cant be 1 ns rise time, because ADL5565 is 7 GHz amplifier. In other side i have 1 ns hold and 1 ns track from master THA, so it should be enough for 700 MHz ADC. Am I right?
I cant put signal direct to HMC760 at this moment. Cant show what I have at input and output of THA. Only with probes maybe.
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