A new frequency compensation technique for three stages OTA by differential feedback path

Abstract

A new single Miller capacitor for frequency compensation of three-stage amplifier is proposed in this paper. In this scheme, a differential stage in which its negative and positive inputs are connected to the output and input nodes of third stage with a cascade capacitor forms the compensation block of a conventional three-stage amplifier. Analysis shows that this configuration significantly improves the frequency domain performances of total circuit such as phase margin (PM) and gain-bandwidth product (GBW) with just a very small amount of compensation capacitor. A three-stage amplifier has been simulated with and without a differential feedback path in a 0.18 μm complementary metal-oxide-semiconductor (CMOS). The simulated amplifier with a 100 pF capacitive load achieved more than 9 MHz GBW and 83°PM while the compensation is less than 0.2% of load capacitor. An amplifier based on conventional nested Miller compensation can just achieve less than 0.23 MHz GBW with the same load, while using more than 100 pF as compensation capacitor. So this method shows an improvement of a factor of 40 in GBW and reduction of a factor of 550 in the size of compensation capacitor. It is a suitable strategy for ON-CHIP compensation in comparison to other methods.

A high‐performance CMOS four‐stage amplifier

“…Usually, in a first step, load capacitor is fixed. Then, (5) and (6) have to be equal by determining Cc, g 4 , and r f . Here, tradeoffs are important to reach acceptable figure of merits (FOMs).…”

“…Additionally, first pole is estimated by (4) that is related to the compensation capacitor, differential block gain, and DC gain, while second pole is due to load capacitor and g m4 that is expressed as (5). Also, the single zero of the structure is defined by compensation capacitor and output impedance of differential block.…”

“…For conventional structures, the low‐voltage regime and technology advancements hamper the development of miniaturized amplifiers. In contrast, multistage amplifiers has been reported to possess excellent response regarding advancements of CMOS technology . We know that over the past years, because of technology advancements, the supply voltage has undergone major reduction without any significant intervention on threshold voltage.…”

“…In contrast, multistage amplifiers has been reported to possess excellent response regarding advancements of CMOS technology. [2][3][4][5][6][7][8][9] We know that over the past years, because of technology advancements, the supply voltage has undergone major reduction without any significant intervention on threshold voltage. So cascode structures are not compatible with low-supply voltages and submicron fabrication, while multistage structures provide high direct current (DC) gain easily.…”

Nonlinear current source charge scheme for comparator based switched capacitor integrator

“…While cascode approach is not compatible with low voltage operation due to voltage swing reduction . And also more importantly multistage designs need frequency compensation to avoid instability issues …”