Hello, I am trying to find out the minimum/maximun input power of the ADC LTC2284. I know that the maximum input voltage is 1 Volt, 0.707Vrms, but what is the input impedance? so that I can calculate the maximum input power as:
minimum input power (SNR ADC) = Maximun input power ( [(0.707)/(2^14))^2]/Rin) + 72.4 dB = Maximun input power Am I right? Many thanks, Jorge On 19 October 2010 19:18, Marcus D. Leech <[email protected]> wrote: > On 10/19/2010 12:21 PM, Jorge Miguel wrote: > > Hi Marcus! > > How do you get the 85 dB value? Is the Intermodulation distorsion of the > page 3 ADC datasheet? > > In the "features" list for the LTC2284: > > 72.4dB SNR, 88dB SFDR > > SFDR is "spur-free dynamic range". > > > > I am not an expecienced engineer (I am recent graduated) but I was thinking > about the maximun and minimum input powers to be linearly detected in the > USRP receiver. > > > > I thought the ADC as a good point to start with and then see what is going > on in the XCVR2450 transceiver > > At the ADC point, it is said that is has 2volts p-p dynamic range. This > value can give us the maximun power input at the ADC provided the input > impedance.(Good question. What is the input impedance? I cannot see it in > the ADC datasheet) > > > > P=(V^2)/R > > Is it right? In other post I can read:*"ADC's datasheet, we need 2Vp-p to > fully utilise its dynamic range. The input impedance of the ADC is around > 220ohms so this is equal to an input signal level of about 6dBm. If you go > above this you will get saturation."* > I do the calculations and it doesn't match!!! > > The LTC2284 can be configured for either 1VP-P or 2VP-P. I believe the > USRP2 uses 1VP-P configuration. > > Generally, with ADCs, you ascribe roughly 6dB of dynamic range per bit, > this is a 14-bit A/D. > > > > Before the ADC is the XCVR2450, with all RF components. Each one of then > has its Noise figure and some of them gain such us the power amplifier or > the Maxim. > > You said that *"The XCVR2450 does have gain control, but it is solely > under control of the host software"*. Besides the ones I mentioned, is > there any other place with gain? > > The MAX2829 has roughly 93dB of RX gain-control range--that's right on the > data sheet, and is "exposed" to the API inside Gnu Radio. > When you create a source, you can specify the gain (actually, you can > change it dynamically as well). > > > > > > Is it the correct way of calculating the dynamic range? > I really need help. > > Thanks, > Jorge. >> >> >> > The LTC2284 A/D is a 14-bit A/D. The maximum input voltage the way it's > configured is 0.707Vrms. Divide that by the > 2^14, and that's roughly your minimum input voltage. In general, though > you take a little bit off the top and add a little > bit onto the bottom of the range. > > > Google is your friend. I'd suggest looking up "ADC noise floor dynamic > range". Plenty of articles out there. > > > > -- > Marcus Leech > Principal Investigator > Shirleys Bay Radio Astronomy Consortiumhttp://www.sbrac.org > >
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