Abstract
A fully differential Miller op-amp with a composite input stage using resistive local common-mode feedback and regulated cascode transistors is presented here. High gain pseudo-differential auxiliary amplifiers are used to implement the regulated cascode transistors in order to boost the output impedance of the composite input stage and the open-loop gain of the op-amp. Both input and output stages operate in class AB mode. The proposed op-amp has been simulated in a 130nm commercial CMOS process technology. It operates from a 1.2V supply and has a close to rail-to-rail differential output swing. It has 156dB DC open-loop gain and 63MHz gain-bandwidth product with a 30pF capacitive load. The op-amp has a DC open-loop gain figure of merit $FOM_{AOLDC}$ of 174 (MV/V) MHz pF/ $\mu \text{W}$ and large-signal figure of merit $FOM_{LS} $ of 3(V/ $\mu \text{s}$ ) pF/ $\mu \text{W}$ .
Highlights
Increasing demands for battery-operated portable electronics equipment like smartphones, wearable medical gadgets, and internet of things (IoT) devices drive the demand of IC’s operating at low voltages and low power and in some applications with high speed
The cascoded flipped voltage follower (CASFVF) operates as a DC level shifter. It sets accurately the voltages VX1, VX1 and VY 1, VY 1 to the reference values VX1 = VX1 = Vref −X1 and to VY 1 = VY 1 = Vref −Y 1 in conjunction with the single-ended amplifiers using negative feedback. This is very important in order to ensure that all transistors in the composite input stage operate in saturated mode within the constraint of the 1.2V total supply used
SIMULATION RESULTS The proposed op-amp was simulated with Cadence Design Framework II using commercial 130nm CMOS technology parameters provided by MOSIS [18]
Summary
Increasing demands for battery-operated portable electronics equipment like smartphones, wearable medical gadgets, and internet of things (IoT) devices drive the demand of IC’s operating at low voltages and low power and in some applications with high speed. This increases the open-loop gain of the op-amp by the factor AAux to a value AOLDC ≈ ((Ai)3/4)AAux. Other high gain approaches based on regulated cascode transistors have been reported in [10]–[12]. The RLCMFB in the first stage boosts the gain-bandwidth product (GBW) and the open-loop gain by approximately a factor 3 and provides class AB operation at the internal nodes Vo1, Vo1’ at the output of the composite input stage. These selections result in M + 1 ≈ 2.4, which leads to peak currents with values IMN 1max ≈ 6IbiasMN 1Q ≈ 6I bias ≈ 168 μA at nodes Vo1,o1
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