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OPA604: voltage follower's gain peeking of OPA2604

Part Number: OPA604
Other Parts Discussed in Thread: OPA2604, , OPA1642

Hello,

My customer plan to use OPA2604 for voltage follower. However customer has concern for the simulation result. This result indicated that frequency response has gain peeking and they would like to reduce this peek. Therefore they requested me the counter measure of this phenomena.

 

I though the best of counter measure is gaining noise gain. In other words, Add the resistance between Inverted Input and Non-Inverted Input.

Is this solution is best for this phenomena? I would like to know your advice for this solution or the other solution.

Thanks and best regards,
Kazuki Kuramochi

  • Kuramochi-san,

    The OPA2604 is a legacy audio op amp, and I am not finding a datasheet for it on TI.com. Everything indicates that it is no longer available from TI and I found this note on the Mouser, an electronics distributor, site regarding the OPA2604, "Restricted Availability: This part number is not currently available from Mouser. Product may be in limited distribution or a factory special order." Therefore, you may have difficulty acquiring the device - especially in production quantities. The single op amp OPA604 still appears to be available, but it too is a legacy device.

    Gain peaking for a unity gain buffer that uses a wide bandwidth op amp such as the OPA2604 is not unusual. The peaking is associated with the phase margin of the op amp used in a particular circuit. Peaking indicates lower phase margin and is akin to the peaking that occurs in an underdamped second-order system. When I run the model as a unity gain buffer I observe about 5.5 dB of peaking, which is equivalent to a little over 30 degrees of phase margin. The phase margin would have to be closer to about 65 degrees to have no peaking. Most op amps are targeted to have a phase margin or 45 degrees, or more, but some do have less.

    I checked the OPA2604 Spice model listing and it was developed over 25 years ago. It uses a simple Boyle model based primarily on two JFET devices. Likely, the model only approximates the ac performance of the actual device. The peaking may, or may not be real. The only way to know for sure if the OPA2604 does what the simulation indicates is to set up your circuit on the bench and check it.

    I suggest that you don't use the OPA2604. There are much newer devices that provide very good audio performance and have very good, modern simulation models available that produce accurate responses. The OPA1642 would be a good choice to replace the OPA2604. You can see the simulation results when I run each of them together as unity gain buffers.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • Kuramochi-san,

    Did the information I provided resolve your OPA2604 voltage follower peaking questions? If so, please close this E2E inquiry.

    Regards, Thomas
    Precision Amplifiers Applications Engineering