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This paper presents the design and implementation of an analog-to-information converter (AIC) capable of Nyquist and compressed sensing modes of operation. The core of the AIC is a 10-bit edge-triggered charge-sharing SAR ADC with a figure of merit (FOM) of 55 fJ/conversion-step and Nyquist-sampling rate of 9.5 Msample/s. The integration of a pseudorandom clock generator enables compressed sensing operation via random sampling and subsequent asynchronous successive approximation conversion by the core ADC. The AIC allows complete reconstruction of a spectrum consisting of sparse single tones or sparse frequency bands using compressed sensing algorithms based on ℓ1-minimization as well as ℓ1,2 regularization, which exploits group sparsity. Implemented in 90 nm CMOS, the prototype SAR ADC core achieves a maximum sample rate of 9.5 MS/s, an ENOB of 9.3 bits, and consumes 550 μW from a 1.2 V supply. Measurement results of the AIC demonstrate an effective bandwidth of 25 MHz, which is 5 × greater than Nyquist-sampling rate with an improved effective FOM of 12.2 fJ/conversion-step for signals with sparse frequency support.