This paper reports a bang-bang clock and data recovery circuit (BBCDR) with an ultra-wide capture range. The circuit exhibits automatic frequency capture and phase locking over a wide 6-to-38 Gb/s range without using a frequency detector, allowed by a recently proposed deliberate-current-mismatch technique. Moreover, we accurately obtain an eight-phase clock through analog interpolation of quadrature signals over the whole wide frequency range by introducing a tunable capacitor array before an inverter-based phase interpolator. A 65-nm prototype of the developed BBCDR occupies an area of 0.07 mm and attains a bit error rate of less than 10 under a continuously variable input frequency, with a total power consumption of 24.6 mW for a 32-Gb/s non-return-zero input, thus leading to 0.769-pJ/bit energy efficiency.