A compact instrumentation amplifier for MEMS thermal sensor interfacing

Abstract

A compact CMOS instrumentation amplifier,\ud based on a properly modified second order Gm–C low pass\ud filter (LPF), is proposed as a possible readout channel for\ud integrated thermal sensors. Low noise and low offset\ud characteristics are obtained by applying chopper modulation\ud to the input transconductor. The high input thermal\ud noise density, typical of low frequency Gm–C filters, has\ud been significantly reduced by adopting a two-stage topology\ud for the first transconductor. Using this approach, an\ud input noise density adequate for thermal sensor interfacing\ud was obtained with no need of off-chip capacitors. The\ud intrinsic filtering property of the amplifier effectively\ud rejects the modulated offset ripple, allowing direct connection\ud of the amplifier output to a low sampling rate AD\ud converter. An original switching strategy involving swapping\ud of the input and feedback ports is used to improve the\ud gain precision. The effectiveness of the technique is proven\ud by means of analytical arguments and electrical simulations\ud performed on a prototype, designed with the STMicroelectronics\ud BCD6s process

A Novel High-Precision Digital Tunneling Magnetic Resistance-Type Sensor for the Nanosatellites’ Space Application

“…Although the differential output voltage signal of the TMR sensors (V in ) can be as small as a few millivolts, the common-mode (CM) voltage V CM depending on the application can be much larger and even vary at the range of a few volts during the operation, as shown in Figure 3 b. To accommodate this variable CM voltage, an Instrumentation Amplifier is generally used for the read-out circuit of the sensors [ 17 , 18 , 19 ]. To accurately process the millivolt-level signal of the TMR sensor, the input referred error of the current feedback instrumentation amplifier (CFIA) should be at the microvolt or nanovolt-level [ 20 , 21 , 22 , 23 , 24 ].…”

CMOS Interfaces for Internet-of-Wearables Electrochemical Sensors: Trends and Challenges

“…A more advanced architecture, shown in Figure 8b, avoids the use of a low-pass filter by combining advanced chopper-stabilized In-amps, capable to auto-suppress the offset ripple, and the eventual use of continuous-time ∆Σ-modulator which has intrinsic anti-aliasing characteristics [107]. Regarding advanced In-amps, a variety of solutions has been proposed in the last several years comprising selective band-pass In-amps [108] and current-feedback amplifier topologies featuring: ripple rejection feedback loops [109][110][111][112], use of switched-capacitors (SC) filters [113,114], ping-pong autozeroing [115], embedded low-pass filter [116,117] or digital calibration techniques [118,119]. Among all these techniques, the digitally-assisted solutions [118,119] proved to be the more efficient in terms of area and power.…”

A Chopper Instrumentation Amplifier With Input Resistance Boosting by Means of Synchronous Dynamic Element Matching

“…Comparing this expression with (3), it is apparent that the impedance boosting is effective for signals well within the amplifier bandwidth, where H(f) is close to one, while the actual advantage gradually decrease as the amplifier cut-off frequency is approached. Note that swapping the input and feedback signals is equivalent to swapping the input transconductors, similarly to the DEM technique proposed in [14][15][16] as a method to reduce the impact of Gmi/Gmf mismatch on the gain accuracy. However, if fDEM is a submultiple of the fch (e.g.…”

“…For this method to be applicable, the output voltage should be free from ripple; furthermore, the common mode voltages of the input and feedback signals should be as close as possible. To reject all contributions to the output ripple, an amplifier with a second order low pass frequency response has been designed [15,16], while the input and feedback common mode voltages are equalized by means of a closed loop approach [17]. So far, experimental demonstration of the mentioned techniques was not provided yet.…”