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OPA2832: How to generate 100K~200khz SINE waveform

Hale Tan
Expert 3360 points
Part Number: OPA2832
Other Parts Discussed in Thread: OPA860, OPA861, OPA615, PGA849, PGA870

Tool/software:

Hi team,

My customer has 2 requirement about SINE waveform design:

1. 120Khz, 3mA peak SINE waveform. Could you help provide a TINA simulation? https://e2e.ti.com/support/amplifiers-group/amplifiers-internal/f/amplifiers-internal-forum/1391466/opa2832-how-to-generate-40mhz-sin-waveform In above link, we can see how to generate SINE waveform, but its output is voltage, not current while the customer requirement is current type output. And in this simulation, could we just use RC circuit to generate SINE waveform? Also could you help provide a formula of SINE amplitude and frequency?

2.100k~200khz, 10mV~100mV SINE waveform. In this requirement, the challenge is that the customer need to adjust amplitude and frequency, not fixed value. Do you have any suggestion how to use amplifier to realize it?

  • 0
    TI__Mastermind 25735 points

    Hello Hale, 

    1. For 120Khz, 3mA peak SINE waveform, do they have an input, or is it similar to the original thread where the device needs to generate this signal? I would suggest using the circuit similar to what was shown in the original thread, and follow it up with another amplifier that would be similar to this application: https://www.ti.com/lit/an/sboa437a/sboa437a.pdf?

      For high-speed versions, I would have recommended our OTAs such as the OPA860, OPA861, and OPA615. Customer can still take a look at these if they want a more integrated version.

      Does the above make sense in terms of application? If so, we can work on making a simulation for this type of circuit. 

    2. Does this need to be generated as well, or will customer be providing an input? Will this be a discrete solution or will they need integrated one chip solution like from from a MCU? I ask, because we commonly only see fixed frequency generators then can be followed by AGC to adjust amplitude depending on input. However, this seems a bit more complicated. 

    Thank you,

    Sima 

  • 0 in reply to Sima Jalaleddine
    TI__Expert 3360 points

    Hi Sima,

    Thanks for your suggestion.

    1. Do you have the TINA simulation which can be shared about Improved Howland Current Pump? And about the 1st SINE voltage waveform simulation, could we use RC circuit to realize? And could you help share the formula with us?

    2.This is a system design. The customers have a back-up solution. It uses MCU to generate square waveform and use op-amp to convert it to SINE wavef7orm. So the frequency is adjusted by MCU and amplitude is adjusted by potentiometer. 

    They need to use this signal to transfer some information so frequency is not fixed. So need to know whether we have any better solution. 

  • 0 in reply to Hale Tan
    TI__Mastermind 25735 points

    Hello Hale,

    1. You mean instead of the original simulation using Colpitts Oscillator, customer wants to use RC oscillator? This could work since frequency is much lower for this solution. But, this would be a voltage output. For Howland current pump solution, I should be able to do this by tomorrow. I would think they would need a precision amplifier for the improved Howland current pump solution. Does customer have any precision needs?

    2. Thank you for the details! Are we trying to displace this back-up solution with a discrete solution? 

    Thank you,
    Sima

  • 0 in reply to Sima Jalaleddine
    TI__Expert 3360 points

    Hi Sima,

    Sima Jalaleddine said:
    You mean instead of the original simulation using Colpitts Oscillator, customer wants to use RC oscillator

    1.RC circuit is easy to realize and size can also be acceptable. Could you help explain the reason why LC can be better than RC? And could yo help share more files about the oscillator principle?

    2.Actually, we just want to know whether we have some other suggestion, not sure this solution is a good option. Because potentiometer from TI doesn't publish new devices for a long time. So we are a little worried there will be no new roadmap for next gen products.

  • 0 in reply to Hale Tan
    TI__Expert 3360 points

    Hi Sima,

    Looking forward to your reply.

  • 0 in reply to Hale Tan
    TI__Mastermind 25735 points

    Hello Hale,

       Sorry for confusion in the last reply. RC oscillator can be used for the first stage for sine-generation, this will be sine-wave output voltage. The second stage can be the Howland Current Pump as the voltage-controlled current source. In this case, precision amplifier, now LVAC team, will help with these designs. I was going to reroute you to the team, but it looks like you made a new thread with them to help create an RC circuit. They will help create the Howland current pump as second stage. Thank you for doing this. 

       For second one, I would have to look into this a bit more. I should be able to get back to you by end of day today.

    Thank you,
    Sima

  • 0 in reply to Sima Jalaleddine
    TI__Mastermind 25735 points

    Hello Hale,

      Update on the second issue. We do not have a discrete solution to offer for switching frequencies. But, if customer is worried about just the potentiometer, then customer should keep MCU then follow this up with a VGA/PGA (variable/programmable gain amplifier). For these low frequencies, I would suggest these devices: 

    1. PGA849: New device, is equipped with eight binary gain settings, from an attenuating gain of 0.125V/V to a maximum of 16V/V
    2. PGA870: -–11.5 dB to +20 dB can be adjusted in 0.5-dB gain steps through a 6-bit control word applied to the parallel interface. This device is higher speed, but I am guessing customer would prefer to digitally control gain (PGA) rather than voltage controlled gain (VCA)

       Here is a link to our PGA/VCA portfolio: www.ti.com/.../products.html

    Thank you,
    Sima