With an RMS load voltage of 0dBm (225mV) the RMS output voltage of the OpAmp will be 450mV. Assuming a crest factor of 3, the peak-to-peak output voltage will be 2.7V. If we assume a sinusoidal output, the peak-to-peak drive capability must be 1.3V. If we assume a full-power bandwidth equal to the small- signal bandwidth, the voltage slew rate should be: $2\pi f_\max \sqrt{2} \times 0.45=120V/\mu$s.
With a crest factor of 3, the amplifier needs to drive $\pm 13.5$mA. If we assu,e a sinusoidal output signal, the peak-peak current drive capability should be 13mA.
The DC gain sets the midband accuracy. For an inaccuracy smaller than 20%, we require a DC gain of 15.
If we assume a single-pole, zero output impedance and zero input capacitance OpAmp, the GB product must equal the ratio of the required bandwidth and the gain of the feedback network. This amounts 90MHz.
If the input capacitance of the OpAmp is much smaller than the antenna capacitance, the GB product needs to be larger than the above minimum.
The output impedance of the opamp causes attenuation of the loop gain. As a result, the requirement for the GB product increases. The pole caused by the parallel connection of the load impedance, the output impedance and the feedback capacitance in series with the antenna capacitance, however, will not become dominant.
If we assume white noise, then the spectrum of the input voltage noise should be less than $L_A\frac{C_A}{C_f+C_A}S_{EA}$, where $S_{EA}$ is the antenna referred noise in $\frac{V}{m\sqrt{Hz}}$, $L_A$ is the antenna length, $C_A$ the antenna capacitance and $C_f$ the feedback capacitance. This equals 3.3 $\frac{nV}{\sqrt{Hz}}$.
If we assume white noise, then the spectrum of the input current noise should contribute less than 200nV/rt(Hz) to the antenna-referred spectrum at a frequency of 10kHz. From this is follows that the spectral density of the current noise should be less than $S_{EA_{f\ell}}L_A2\pi f_{\ell}C_A= 40\frac{fA}{\sqrt{Hz}}$. Where $S_{EA_{f\ell}}$ is the antenna-referred noise at the lowest frequency of interest.
See section about biasing. Bias current up to about 5nA (noise limited).
The input of the OpAmp is biased at half the power supply. The offset voltage and bias current do not cause a noticeable change in the load drive capability (See section about biasing).
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SLiCAP: Symbolic Linear Circuit Analysis Program, Version 1.1 © 2009-2022 SLiCAP development team
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Last project update: 2022-04-04 16:00:00