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A sub-1-μs ultrafast-response buck converter utilizing improved analog-voltage-dynamic-estimation (AVDE) techniques is proposed in this letter to improve previous works. First, the improved AVDE controller uses a new pseudocurrent circuit and a new ramp generator to get low gain, wide bandwidth, wide dynamic range, and low equivalent series resistor $(R_{{\text{ESR}}})$ . Second, the proposed converter has high performance, fast transient response, and low output voltage ripple. Third, the circuit does not need slope compensation so that it is very simple to implement. The switching frequency of the proposed buck converter is 1 MHz for nominal 3.3-V input and 0.8–2.5-V output range application. The experimental results prove that the proposed scheme improves the transient response within 1.2 μs and its maximum power efficiency can be up to 91.9%. The fastest transient time of the proposed converter is only 0.8 μs as the switching frequency is equal to 1 MHz. The settling time of the proposed converter is only within 0.8 cycle of the switching frequency. The maximum load current is 300 mA. The proposed buck converter has been fabricated with a commercial 0.35-μm CMOS 2P4M process, and the total chip area is about ${1.46 \;\text{mm}\times 1.5}$ mm, including PADs.