A 4.4μW 2.5kHz-BW 92.1dB-SNDR 3^rd-Order VCO-Based ADC With Pseudo Virtual Ground Feedforward Linearization

A Review on Direct Digital Conversion Techniques for Biomedical Signal Acquisition

“…Despite the fact that other indicators are excellent, a nine-bit CDAC is needed to feedback prediction signal, leading to extra area; in addition, input impedance is limited by chopping frequency and input capacitance. Corentin Pochet proposed a third-order VCO-based ΔΣADC [21] using a pseudovirtual ground feedforward technique. As shown in Figure 12, each integrator is comprised of a Gm stage and VCO followed by PFD.…”

“…The signal current IS through RS and the feedback current IDAC generated by RDAC are subtracted at the VS. Due to the feedback-assisted Gm linearization, the magnitude of the IIN maintains within the LSB of the feedback DAC current even with a large input voltage, which can significantly improve the linearity of the CTDSM system. This design achieves a high input impedance, a 300 mVpp linear input range, a 80.4 dB Corentin Pochet proposed a third-order VCO-based ΔΣADC [21] using a pseudovirtual ground feedforward technique. As shown in Figure 12, each integrator is comprised of a Gm stage and VCO followed by PFD.…”

“…Although other performance values are excellent, the input impedance (4 MΩ) is limited by the chopper and input capacitor. In [21], a third-order VCO-based DSM was proposed using a pseudo-virtual ground to eliminate the large swing at the integrator output. This work also achieves good tradeoff between SNDR (92 dB) and power (4.4 µW), but input impedance is poor.…”

“…Compared to the traditional DDC structure, the VCO-based DDC structure can achieve higher SNDR and FOM more easily because it has larger input range and displays lesser quantizer power consumption. The linearity of closed-loop structures is better [19][20][21][22] compared to the open-loop VCO-based structures in [18]. An obvious advantage of higherorder VCO-based DDC [21] is their ability to achieve large input range and high SNDR.…”

“…The linearity of closed-loop structures is better [19][20][21][22] compared to the open-loop VCO-based structures in [18]. An obvious advantage of higherorder VCO-based DDC [21] is their ability to achieve large input range and high SNDR. When input impedance is the primary requirement, chopper-less designs [18,22] exhibit excellent performance at the cost of low-frequency noise.…”