Bias-adaptive cross-coupled CMOS MAGFET pair for bipolar magnetic field detection

Abstract

In the conventional cross-coupled CMOS magnetic fieldeffect transistor (MAGFET) pair, at least one MAGFET is self-biased. The output swing at. the self-biasd end is then inevitably limited to the threshold voltage of the self-biased MAGFET. This problem emerges for bipolar magnetic field sensing. In this paper, we propose a bias-adaptive voltage level shifter to remove the direct self-bias connection between the gate and the drain and to adjust the operating point at the output node, so as to achieve symmetric yet maximum positive and negative output swings. The improvements have been verified by HSPICE simulation.

A novel 0.7 V high sensitivity complementary differential MAGFET sensor for contactless mechatronic applications

“…Similarly, exactly the opposite is happening at the cross-connection of drain2 of the NMAGFET and the drain1 of the PMAGFET (at terminal B) where the voltage is going up by two mechanisms. The difference in the voltage between the two cross connections (voltage at terminal A-voltage at terminal B) which is the V SENSE of the proposed composite CDMAGFET is now going down by 4 mechanisms compared to 2 mechanisms in the case of the CCMAGFET [21,11] and the sensed voltage is double that of [21,11]. This is also clear from Fig.…”

“…As a result with increasing magnetic field intensity, the differential voltage between the terminal A and the terminal B of the proposed CDMAGFET increases significantly compared to that in case of just a NMAGFET. In a previously reported CCMAGFET [11] the output is only single-ended, and the current variation in only one set of cross-coupled drains is used for sensing, while, the current in the other cross-coupled pair is wasted. Whereas, in the CDMAGFET (fully complementary, cross-coupled and differential MAGFET) described here, currents in both the cross-coupled pairs are used for sensing, and the output sensing signal is a differential voltage providing improved bipolar detection compared to the CCMAGFET [11] without the need for level shifting, as well as providing approximately twice the sensitivity of the CCMAGFET of [11] for the same geometry and process technology.…”

“…The current in the drain1 of both the NMAGFET and the PMAGFET increases (by + in and + ip, respectively) and decreases (by − in and − ip, respectively) at the same time (are in phase), while the current in the drain2 of both the NMAGFET and the PMAGFET increases and decreases by same amount of the steering small signal currents at the same time (are in phase, and 180 • outof-phase with the currents in the drain1 of both the NMAGFET and PMAGFET). This is the reason why the split drains of the NMAGFET and the PMAGFET are cross-coupled, so that the voltage at each cross-connection goes up or down by two mechanisms (instead of one mechanism in case of a NMOS or PMOS only MAGFET), as is in the case of the CCMAGFET [11] which uses one crossconnection for sensing. This can be seen from the current-flow circuit of the CDMAGFET in Fig.…”

“…The voltage V diff is applied across a differential pre-amplifier with a dynamic current mirror load, which also converts the CDMAGFET output into a single ended voltage which is then provided as a sensed voltage through a source follower. In [11,21] differential-to-single-ended converter is built-in in the CCMAGFET thus sacrificing the extra sensitivity that can be achieved by a fully differential output. The overall sensed voltage V SENSE of the sensor is then given by: (1/g m 10 ) + 1/((1/r o 10 ) + (1/r o 11 ) + g mb 10 )…”

“…In this paper a novel low-voltage MAGFET modification is presented consisting of the cross-coupling and differential operation of a NMOS and a PMOS MAGFET resulting in enhanced sensing of the magnetic field intensity orthogonal to the MAGFET plane. It is found that the magnetic field sensitivity can be increased significantly by using this modification compared to that using only a singleended NMOS MAGFET or a single-ended cross-coupled MAGFET (CCMAGFET) [11] for the same geometry and process technology. Both simulation and experimental monolithic silicon implementation are discussed in this paper verifying the improvement in magnetic field sensing and the potential for practical contact-less mechatronic applications of the proposed modified MAGFET sensor in today's low-voltage nanometric CMOS.…”