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Table 2 Values of filter amplifier circuit components. Resistor values (R) are in [?]; capacitor values (C) are in [F]. Components' names refer to Figure 2. In order to avoid loading the filter, the circuitry must guarantee that the impedance of sources to the filter is low and the impedances of sinks are high. The output impedance Lonafarnib in vivo of the preamplifier stage is VAV2 amplifier for both the active and low-pass filter is OPx177 (Texas Instruments), which is a low-noise (8?nV/��Hz at 1?kHz), low-offset (selleckchem amplifier was chosen. Even though this results in an increase of the noise level of filter amplifiers, input-referred noise of filter amplifier is negligible compared to preamplifier output noise level, as confirmed by simulations (i.e., ~1.5?��V RMS versus ~70?��V RMS). 2.2.3. Overall Response The overall response provides a gain of ~1100, similar to other circuits in the MEA literature [9, 12, 14, 21, 28] and in commercial devices (Multi Channel Systems GmbH, Axion Biosystems Ltd.). The whole frequency band is delimited by 2 high-pass poles (i.e., slope equal to +40?dB/decade) and 4 low-pass poles (i.e., slope equal to ?80?dB/decade). The ?3?dB point of the entire system can be calculated from the product of each stage's transfer function. This yields systemwide ?3?dB points at 300?Hz and 3.03?kHz, which respects the bandwidth requirements. The frequency of 12?kHz is attenuated by 40?dB compared to the frequencies in the pass band, which suggests a minimum sampling frequency of 25?kHz, as commonly done with MEA recordings [25]. A 50?Hz signal at the preamplifier input is amplified by a factor of 10, which is 40?dB less (i.e., 100 times less) than the gain in the pass band. Further attenuation of the 50?Hz interference is typically left to digital filters.