OPA827: The output voltage question for OPA827

Mickey Zhang

Genius 12080 points

Part Number: OPA827

Hi team,

I have a question for 5.1. TI Precision Labs - Op Amps: Bandwidth 1. In this video, the input signal frequency is 200kHZ, the closed gain

is set to 100V/V. The GBW for OPA827 is 22MHZ. So, 200kHZ*100V/V=20MHZ<22MHZ, So, the 200KHZ input signal can be

normally amplified 100 times. That is when the input signal is 200KHZ, the closed gain should be 100V/V, correct?

But in TINA circuit, it shows the closed is 37.75dB when the input signal is 200KHZ. Would you explain this?

over 6 years ago

0 Mickey Zhang over 6 years ago

TI__Genius 12080 points

Hi team,

Would you explain this?

0 Tim Green1 over 6 years ago in reply to Mickey Zhang

TI__Expert 6275 points

The gain bandwidth formula is: GBW = Gain * BW
So for G=1 on OPA827, GBW = 22MHz . G * BW = 22MHz. 1 * 22MHZ = 22MHz. For a -20dB/decade Aol slope like on OPA827 GBW = constant
So now for G=100 on OPA827: 22MHZ = 100 * 220kHz
So closed loop gain of 100 will have a closed loop Vout/Vin -3dB frequency at 220kHz.
Simulated Measure closed loop AC gain at 100 shows closed loop gain of 37.7dB at 200kHz which makes sense since at 220kHz we would predict 37db (or -3dB down from 40dB)

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OPA827: The output voltage question for OPA827