OPA656 is a broadband, unity gain stable, field-effect transistor input operational amplifier 9

Generally speaking, before the fundamental wave reaches a very high frequency or power, the second harmonic will control distortion with a negligible third harmonic component. Then, focus on the second harmonic and increase the load impedance to directly improve distortion. Please remember that the total load includes the feedback network in non-invasive configuration, which is the sum of RF+RG, while in reverse configuration, this is only RF (see Figure 1). The increase in output voltage swing directly increases harmonic distortion. diode An increase of 6dB in output swing typically leads to an increase of 12dB in 2nd harmonic and 18dB in 3rd harmonic. Increasing signal gain also increases 2nd harmonic distortion. By increasing the gain by 6dB, even if the output power and frequency remain constant, the 2nd and 3rd harmonics will increase by about 6dB. Finally, due to the attenuation of the loop gain with frequency, the distortion increases with the increase of the fundamental frequency. On the contrary, distortion will improve to the main open-loop pole at lower frequencies around 100kHz. Starting from the second harmonic of -70dBc (5MHz), the 2VPP fundamental becomes a 200 Ω load at G=+2 (typical characteristic), and the distortion of the second harmonic below 100kHz will be less than -105dBc.diode

OPA656 has extremely low third-order harmonic distortion. This is also shown in the 2-tone third-order intermodulation pseudomodulation (IM3) response curve. At low output power levels, the third-order false level is extremely low (<-80dBc). Even if the basic power reaches a higher level, the output stage remains at a low level. Typical features indicate that the false intermodulation power does not increase as predicted by traditional interception models. As the basic power level increases, the dynamic range does not significantly decrease. For two tones centered at 10MHz, 4dBm/tone to a matched 50 Ω load (i.e., 1VPP per tone at load, and 4VPP required for the entire 2-tone envelope at the output pin), the typical characteristic shows a 78dBc difference between the test tone and the third-order intermodulation false level. When operating at low frequencies and/or higher load impedances, this special performance is further improved.diode

DC accuracy and offset control

OPA656 has the advantages of high open-loop gain, high common mode rejection, high power supply rejection, small input bias voltage (drift), and negligible error in input bias current, which can provide excellent DC accuracy. In order to achieve the best DC accuracy, high-level versions (OPA65UB or OPA656NB) filter key DC parameters to stricter limits. Both the standard and high-level versions utilize new final testing techniques, with 100% testing of input bias voltage drift exceeding temperature. This discussion will use advanced typical and minimum/maximum electrical characteristics to illustrate; However, the standard level version applies the same analysis.diode