# Enhancing Meteor Observations with Photodiode Detectors
## 3 Concept
### Noise Analysis  
Our analysis indicates that, excluding the diode itself, the dominant noise contributors in the detector are the thermal noise of resistor R2 within the transimpedance amplifier, the equivalent input noise voltages of amplifiers U2 and U3, as well as the equivalent input noise current of amplifier U2. Other sources, including the thermal noises of the resistors in the low-pass filter, are considered negligible. Table 2 presents the values of the predominant noise sources along with their impact on the mean square voltage at the detector's output. Based on the information from Table 2, we can deduce that the most significant source of noise is thermal noise, which has a value of \(3.2\times 10^{-11}\frac{\mathrm{V}^{2}}{\mathrm{H}_{2}^{2}}\) for the resistor R2 and the voltage noise of Reference U1. The effective voltage of the noise at the output is obtained by multiplying the RMS voltage by the bandwidth and rooting. Assuming an effective bandwidth of 25 Hz, we obtain an output noise RMS value of \(\sigma_{\mathrm{R+}t\mathrm{I}1}=37.7\) uV. One can see that this value is more than an order of magnitude lower than the resolution of the A/D converter used, 1.22 mV. The internal noise associated with A/D conversion and with the IIR filter on, were measured by disconnecting the diode module from ADuC microcontroller and connecting reference 1.2 V, stable DC voltage, to the A/D converter inputs. We measured the RMS digital signals received from the IIR filter at \(\sigma_{ADC+IIR}=27\) uV. Eventually, the expected noise level of our detection circuit should be \(\sigma_{total}=\sqrt{\sigma_{\mathrm{R+}t\mathrm{I}1}^{2}+\sigma_{ADC+IIR}^{2 }}=\sim 46\) uV. It should be emphasized that this is the lower limit of the noise level that one expects to see in the final detection circuit. The estimated noise levels lead to the conclusion that the system has been designed to maintain minimal intrinsic noise. The noise level post-A/D conversion is comparable to the largest noise component in the analog signal path, indicating that there is no unnecessary or unwanted amplification of the measurement noise. This outcome underlines the effectiveness of our design in preserving the integrity of the signal, ensuring that the \begin{table}
\begin{tabular}{l c c} \hline
**Source** & **Mean Square Voltage or Current** & **Output Mean Square Voltage** \\ \hline Thermal Noise R2 & \(V_{R2}^{2}=4 kTR2=3.2\cdot 10^{-13}\frac{\mathrm{V}^{2}}{\mathrm{H} _{2}^{2}}\) & \(V_{0R2}^{2}=3.2\cdot 10^{-11}\frac{\mathrm{V}^{2}}{\mathrm{H}_{2}^{2}}\) \\ Input Voltage Noise of Amplifier U2 & \(V_{n2}^{2}=(25\cdot 10^{-9})^{2}\frac{\mathrm{V}^{2}}{\mathrm{H}_{2}^{2}}\) & \(V_{0m2}^{2}=6.25\cdot 10^{-14}\frac{\mathrm{V}^{2}}{\mathrm{H}_{2}^{2}}\) \\ Input Current Noise of Amplifier U2 & \(I_{n2}^{2}=(2\cdot 10^{-15})^{2}\frac{\mathrm{V}^{2}}{\mathrm{H}_{2}^{2}}\) & \(V_{0i2}^{2}=1.6\cdot 10^{-13}\frac{\mathrm{V}^{2}}{\mathrm{H}_{2}^{2}}\) \\ Input Voltage Noise of Amplifier U3 & \(V_{n3}^{2}=(25\cdot 10^{-9})^{2}\frac{\mathrm{V}^{2}}{\mathrm{H}_{2}^{2}}\) & \(V_{0n3}^{2}=6.25\cdot 10^{-14}\frac{\mathrm{V}^{2}}{\mathrm{H}_{2}^{2}}\) \\ Voltage Noise of Reference U1 & \(V_{n1}^{2}=(500\cdot 10^{-9})^{2}\frac{\mathrm{V}^{2}}{\mathrm{H}_{2}^{2}}\) & \(V_{0n3}^{2}=2.5\cdot 10^{-11}\frac{\mathrm{V}^{2}}{\mathrm{H}_{2}^{2}}\) \\ \hline \end{tabular}
\end{table} 
Table 2: Main noise sources and their estimated values. noise characteristics are predominantly determined by the inherent properties of the analog components, rather than by the digital conversion process. To verify the noise level under real-world conditions, one photodiode was fully shielded from light, allowing us to capture the system's inherent noise. A 10-s segment from sample night observations was chosen for the noise power analysis. During this time, the signals on the light-detecting diodes were least noisy, i.e., devoid of any abrupt brightness spikes that could arise from various external sources.