making a High Gain, High Speed wide-band Amplifier by AD8067

Folks,

I have a question about making a High Speed high Bandwidth Amplifier by AD8067.

if you read page 21 of AD8067 datasheet and see fig.57 you will find a composite amp with gain of 100 and very wide BW making by a AD8067 and a AD8009.

so my question is:

Why we need to using a AD8009 for making this Amp. instead of using just 2 AD8067 with lower gain 10 in series configuration!?

two ad8067 amp with gain 10 in series give us almost same characteristics that composite amp shown in fig.57 of datasheet has.

I highly appericated to read your ideas

TanQ

    •  Analog Employees 
    on Nov 26, 2019 8:45 AM over 1 year ago

    Hi Tan,

    You can refer  to this great article the benefits of having a composite configuration of the amplifier. One of the biggest improvement would be bandwidth extension. Two AD8067 won't achieve the bandwidth that the AD8067 and AD8099 composite configuration offers. The AD8099 has also a very high output capability. It really boils down on your system requirement. The key benefit of having a composite amplifier is preserving the precision of the front-end and having a high output drive capability.

    Regards,
    Goz

  • Dear Gauzz

    TanQ for ur reply

    before your answer, I did some simulations by spice models of two AD8067 in series and a composite of a AD8067 and a AD8009 and found improvements by composite configuration against two series amps.

    now I have an another question.

    would you pls tell me your opinion about using ADA4817 instead of AD8067 with a AD8009 in composite topology?

    becoz ADA4817 has wider bandwith vs AD8067 and composite of ADA4817+AD8009 give me more better phase Error vs composite of AD8067+AD8009 in my desire working frequency.

    are there any issues about precision If I want to using ADA4817 instead of AD8067?

    •  Analog Employees 
    on Dec 3, 2019 7:35 AM 11 months ago in reply to Memet

    Hi,

    Yes, the precision will be affected since the offset voltage, noise and distortion will be higher on ada4817. As I have said previously on my post, it really depends on your system requirements on how you will compensate the limitations of your front-end and your output amp. If you prioritize bandwidth, ada4817+ad8009 would be a good choice.

    May I know what your system requirement are so that we can choose a more suitable part for your application?

    Regards,
    Goz

  • I want to use this composite amplifier for amplifying an under -60dBm level signal (from -60dbm to -150dbm) into -60dbm to 0dbm input range of AD8302 by two 40db stage gain(amplifier)... I described to you the schematics of my desire analog front end circuit for this purpose under "AD8009 Capacitive load Drive Capability".

    below is comparison of AD8067 and AD4817 and seems almost the same but wider BW of AD4817!

  • OK I write it again here about the whole schematic...

    I plane to use AD8009 or AD8007 as last stage buffer of my analog front end circuit before AD8302.

    before AD8009 I have a resistive Attenuator, one AD4817 as a High Speed FET input buffer and a AD8337 as a VGA and then a AD8009/8007 as a buffer between the input circuits and AD8302.

    also my other discussion about AD8067+AD8009 vs AD4817+AD8009 composite amplifier is related to this circuits.

    after these AD8009 buffer, I have another signal path that need to amplify input by 80dB gain and I plan to do it by two composite amp that each has 40dB gain and multiplexed 0dB, 40dB and 80dB by a AD8174 with 0dB gain.

    these high gain stages must be ac coupled in range 20Hz to 50Mhz.