Open Access
Bulk-driven CMOS linear transconductance-cell for AC amplifiers with very low cut-off frequency
(Elsevier, 2023) Ocampo-Hidalgo, Juan J.; Domínguez, Miguel Á.; Cruz Blas, Carlos Aristóteles de la; Carrillo, Juan M.; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
This manuscript proposes a novel linearized transconductor for AC amplifiers with a very low cut-off frequency. The cell uses an alternative solution that is based on a modified source-degeneration OTA, using two bulkdriven buffers, incorporating bootstrapping techniques to a buffer and a degenerated resistor. In the buffer, the bootstrapping effect is implemented by using a pseudo-resistor and a linear capacitor properly configured, whereas in the resistor the output voltages of the buffers are used with this goal. Thus, the proposed solution allows realizing a very large time constant, avoiding the use of very large size resistors and capacitors, thus saving chip area. The technique is demonstrated in an 0.18 μm CMOS technology by designing an OTA operating with a supply voltage of 0.6 V and achieving a low cut-off frequency of around 2 Hz with a power consumption of 462 nW.
Open Access
0.6-V 1.65-uW second-order Gm-C bandpass filter for multi-frequency bioimpedance analysis based on a bootstrapped bulk-driven voltage buffer
(MDPI, 2022) Carrillo, Juan M.; Cruz Blas, Carlos Aristóteles de la; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
A bootstrapping technique used to increase the intrinsic voltage gain of a bulk-driven MOS transistor is described in this paper. The proposed circuit incorporates a capacitor and a cutoff transistor to be connected to the gate terminal of a bulk-driven MOS device, thus achieving a quasi- floating-gate structure. As a result, the contribution of the gate transconductance is cancelled out and the voltage gain of the device is correspondingly increased. The technique allows for implementing a voltage follower with a voltage gain much closer to unity as compared to the conventional bulk-driven case. This voltage buffer, along with a pseudo-resistor, is used to design a linearized transconduc- tor. The proposed transconductance cell includes an economic continuous tuning mechanism that permits programming the effective transconductance in a range sufficiently wide to counteract the typical variations that process parameters suffer during fabrication. The transconductor has been used to implement a second-order Gm-C bandpass filter with a relatively high selectivity factor, suited for multi-frequency bioimpedance analysis in a very low-voltage environment. All the circuits have been designed in 180 nm CMOS technology to operate with a 0.6-V single-supply voltage. Simulated results show that the proposed technique allows for increasing the linearity and reduc- ing the input-referred noise of the bootstrapped bulk-driven MOS transistor, which results in an improvement of the overall performance of the transconductor. The center frequency of the bandpass filter designed can be programmed in the frequency range from 6.5 kHz to 37.5 kHz with a power consumption ranging between 1.34 μW and 2.19 μW. The circuit presents an in-band integrated noise of 190.5 μVrms and is able to process signals of 110 mVpp with a THD below −40 dB, thus leading to a dynamic range of 47.4 dB
Open Access
0.6-V CMOS bulk-driven instrumentation amplifier for IoMT bioimpedance analysis
(Wiley, 2024) Carrillo, Juan M.; Ocampo-Hidalgo, Juan J.; Corbacho, Israel; Cruz Blas, Carlos Aristóteles de la; Domínguez, Miguel Á.; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
An instrumentation amplifier (IA), aimed at wideband bioimpedance analysisin the low-voltage low-power scenario of internet of medical things (IoMT), ispresented. The operation principle is based on the indirect current feedbacktechnique, where an input and a feedback transconductor determine thevoltage gain of the preamplifier. The required transconductors consist of twobulk-driven flipped-voltage-follower cells and an active pseudo-resistor, thusleading to a linear and compact implementation. The circuit has been designedand fabricated in 180 nm CMOS technology to operate with a 0.6-V supply.Experimental results obtained from measurements on eight samples of thesilicon prototype show that when the IA is programmed to have a nominalvoltage gain of 11 V/V, the bandwidth is 316.2 kHz, the CMRR exceeds63 dB, and the maximum output voltage that can be processed with a THDbelow –40 dB is 555 mVpp.
Open Access
Low-voltage CMOS bulk-driven buffer with bootstrapping technique for gain enhancement and THD-noise reduction
(IEEE, 2022) Cruz Blas, Carlos Aristóteles de la; Carrillo, Juan M.; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
In this paper, a bootstrapping technique is applied to a bulk-driven voltage buffer for canceling the gate-source transconductance in order to improve the cell gain, the linearity and reduce the input-referred noise. The bootstrapped circuitry is conveniently implemented by only using a capacitor and a pseudo resistor. The suitability of the technique is demonstrated by simulation results using a flipped voltage follower, even though it is general and can be applied to other structures. A 1-V buffer is designed in 0.18 µm CMOS technology, showing a 4.3 times improvement in the voltage gain (conventional 0.21 V/V, bootstrapped 0.90 V/V), increasing 5 times the input voltage range for a 1% THD (conventional 50 mV, bootstrapped 250 mV) and reducing the input equivalent noise around a 16% (conventional 180 nV/-√Hz, bootstrapped 155 nV/√Hz at 10 kHz).

Cruz Blas, Carlos Aristóteles de la

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