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About the SFDR and THD specification of AD3551R and LTC1668

Category: Hardware
Product Number: AD3551, LTC1668


We find a new DAC of ADI, AD3551R. This might be the right product for our bio-instruments. We would like to generate a tone with high precision (THD>90dB) within the 1KHz to 1.2MHz frequency range, with high precision, high speed and low temperature drift.

1, Figure 33 and Figure 36 only show the THD v.s. frequency within the range of 100KHz, does AD3551R supports generating a tone above 100KHz, i.e., 1MHz tone? What's the specification of SFDR and THD of AD3551R (as well as LTC1668) within the frequency range 1KHz ~ 1MHz? What's the recommended high speed, precision amplifier suggested to be used with AD3551 in the high-frequency end (800KHz ~ 1.2MHz)?

2, We found that LTC1668, page 5, Figure 6, The SFDR v.s. frequency. LTC1668 could generate a single tone of 1MHz with >90dBFS SFDR with a update rate 5MSPS. Is AD3551R superior or inferior to LTC1668 in generating a tone of high frequency, 800KHz ~ 1.2MHz? 

3, which one should I choose for our product, AD3551R or LTC1668?



  • Hi Benuyan,

    We have not concluded the evaluation of the AD3551R above 100 kHz. The AD3551R is capable of generating tones up to half the update rate but overall performance depends on the amplifier, filter and configuration of the DAC.

    From the amplifiers we have tested, the AD8065 would be close to meeting the 90 dBc THD requirement at 1 MHz. We are still testing other options aiming at improving DC and AC performance.

    The main difference in performance between AD3551R and LTC1668 is the noise floor: 20 pA/√Hz vs 50 pA/√Hz. Our preliminary measurements show that the AD3551R would be on par with the LTC1668 in terms of THD at 1 MHz. However there are several adjustments we are testing to improve performance. We aim at publishing an application note with recommendations when the work is concluded.

    Best regards,


  • Hi, Will the reference design of LTC2757/LTC2758 using composite amplifier suit for 1MHz, >90dB THD design for this AD3551R chip?

  • I don't think so. The amplifiers in that design are way too slow, so the output would just oscillate trying to follow the DAC. The topology is probably not adequate since Iout has to dump current into a virtual ground at 2.5V.

    I would recommend a two-stage composite amplifier with ADA4807 as first stage and LT1363 as second stage.

  • Thank you for your support! I compare this two chips, ADA4807 and LT1363,,asc&p4502=50M|4G&d=5047|4501|4089|4095|2687|4502|300|4101|4102|4124|4108|2839|2840|s3|s16|s5&p2687=1&sel=row144|row219

    ADA4807 is superior to all specifications of LT1363 except for the Vs Span MAX. Could we use ADA4807 alone?

    The output of AD3551R is used to drive a Howland VCCS current source injecting ~1mA current in to biological tissues. So the output of AD3551R should be precision, and the span of voltage output can be left to the enhanced howland current source.

  • How about LTC6226/LTC6227?

    I am a little bit puzzled on the selection of DAC output driver buffers for AD3551R, may be I should stick with your upcoming reference designs which features a low distortion solution. Or, could you tell me some design considerations in selecting the right buffers for AD35531R?

    The frequency range is 1KHz~1MHz, so maybe some high-end audio amplifiers could do this?

  • Yes, you may use ADA4807 or ADA4805 if the voltage span is less than 10V. Note that current sourcing / sinking capability is exhausted as the output voltage gets close to the rails. It should be no problem if the Howland amplifier has high input impedance.

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