Floating-bulk transistors: An alternative design technique for CMOS low-voltage analog circuits

Abstract

This letter details a novel floating-bulk transistor technique for low-voltage design. The approach is derived from two previous wellknown techniques: bulk-driven and quasi floating-gate. The floating-bulk technique uses an input capacitive coupling through a floating bulk of a PMOS allowing modulation of the drain current. A fabricated commonsource amplifier was tested on CMOS 0.5 µm technology and the feasibility of the proposal was demonstrated.

Four-quadrant multiplier using the floating-bulk technique for rail-to-rail input range and insensitivity to different input dc levels

“…2a [12] and is based on Flipped-Voltage Followers (FVF) [13], which are marked in square rectangles. Floating-bulk transistor [30].…”

“…The latter eliminates the need for this 𝑉 𝑇𝐻 , yielding to lower supply requirements; however, the signal swing at the bulk terminal must be small to prevent large currents by forward biasing the substrate-source junction of the transistor; it also has found many applications [23]- [29]. A recently reported technique that avoids the aforementioned drawbacks is the Floating-Bulk (FB) technique [30], shown in Fig. 2b.…”

“…3, where the input transistors M1-M6 were replaced with FB transistors marked in dashed rectangles. The operation of M5 is as follows: the input capacitor 𝐶 and the diode formed by the source-bulk junction induce a clamping effect that reflects the ac variations in 𝑉 𝑎 at node a' [30] multiplied by a scaling factor. Small signal analysis shows that the FB technique has a gain of 𝐴 𝐹𝐵 = 𝑔 𝑚𝑏 /(𝑔 𝑚𝑏 + 𝑔 𝑚 ), where 𝑔 𝑚 and 𝑔 𝑚𝑏 are the gate and bulk transconductance gains, respectively.…”

“…Fig.2. a) Multiplier based on the Flipped Voltage Follower[12], and b) Floating-bulk transistor[30].…”

Current‐mode body‐biased switch to increase performance of linear charge pumps

“…However, in the real case, the charge accumulated in the N‐well can flow through the substrate junction, which is reverse biased. By equating the two currents, voltage V DB has to be small (some tens of millivolts) due to exponential dependence on the base current 15 . Such result guarantees that floating body of transistor do not cause any additional current loss during cut‐off.…”