High PSR output-capacitor-less LDO with double buffers technique

A low power external capacitor‐less low drop‐out regulator with low over/undershoot voltage and high PSR

“…The zeroes in the transfer function are created by the frequency compensation and the PSR enhancement circuitry. Based on the simulations and the calculations (i.e., by extracting circuit parameters from Cadence and replacing in (10)), ω po is located after the unity gain frequency. In the proposed LDO's transfer function, it is difficult to simplify the parametric zeros because of the complexity of the numerator.…”

“…In fact, because of the crossmultiplication and summation of different transfer functions, the numerator of ( 10) is complex, and obtaining exact symbolic zeros is not feasible, though approximate location of zeros is a function of circuit parameters as given by (12). Instead, by replacing the circuit parameters in numerator of (10), the zeros are obtained using numerical methods in MATLAB as ω z1 = À3.7, ω z2 = À383.3 and ω z3,4 = À760.7 ± 1427.4 krad/s. The numerical value of all extracted poles and zeros are shown in Figure 14A.…”

“…7,8 However, the use of off-chip capacitors in microfarad ranges in these circuits increases the printed circuit board (PCB) area and the bill of material. 9,10 Recently, some techniques for eliminating off-chip capacitors have been proposed in literature. For example, using a capacitive multiplier instead of an off-chip capacitor 11 and so forth, all the techniques have high complexity and high power consumption.…”

“…In other words, LDOs compensated by off‐chip capacitors have typically better PSR because of the filtering of power supply ripples by the large off‐chip capacitor 7,8 . However, the use of off‐chip capacitors in microfarad ranges in these circuits increases the printed circuit board (PCB) area and the bill of material 9,10 . Recently, some techniques for eliminating off‐chip capacitors have been proposed in literature.…”

“…Figure13shows the small-signal model of the proposed voltage regulator, and (10) is the transfer function obtained by this model in which g m,i and r ds,i are the transconductance and channel resistance of the transistor i, respectively. Equation (11) represents the poles extracted by(10). These poles are generated by the overshoot, undershoot, and feedforward (FF(s)) paths and denoted by ω pos , ω pus , and ω pFF , respectively.…”