A Subhertz Nanopower Low-Pass Filter

Abstract

Abstract-This brief presents a first order low pass filter topology capable of providing cut-off frequencies down to 2 mHz with a power consumption of 5 nW. The circuit is intended for signal conditioning applications, particularly for use with very low frequency physiological signals in low power portable medical equipment. To achieve the low frequency cut-off the filter is based around the use of a clocked transconductor which provides a low transconductance while using a relatively high bias current level. The circuit is implemented in a 0.35 µm technology with a 1 V supply and has a measured 32 µV RMS of noise and 64 dB dynamic range. In terms of power consumption and cut-off frequency the reported filter outperforms previous filters from the literature.

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“…The low cutoff frequency (60 mHz) of the low-pass filter is realized by continuously clocking the output of an OTA cell, as proposed in [28]. The filter operation principle has been shown in Fig.…”

“…In order to allow for direct comparison of the fabricated system performance with [16] The system performance has been summarized in Table IV [28]. …”

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“…Furthermore, since the input signal to the TEO circuit is fairly band-limited (11)(12)(13)(14)(15)(16) to the Sleep spindle frequency range, the low pass filter nearly constant group delay of 4 ms with a 1% variation across the mentioned bandwidth is acceptable.…”

“…5, the transconductor output current (I 1 ) can only flow into the capacitor when the switch is closed. Assuming the clock duty cycle to be δ, the effective current flowing into the capacitor (I 2 ) is defined using (2) [16].…”

“…The measured frequency responses of the 8 Hz to 11.3 Hz and 8 Hz to 16 Hz bandpass filters used in the median frequency comparison circuit has been shown in Fig. 12.…”