Sampling Circuits That Break the kT/C Thermal Noise Limit

Several circuit-level techniques are described which are used to reduce or cancel thermal noise and break the so-called kT/C limit. kT/C noise describes the total thermal noise power added to a signal when a sample is taken on a capacitor. In the first proposed technique, the sampled thermal noise is reduced by altering the relationship between the sampling bandwidth and the dominant noise source, providing a powerful, new degree of freedom in circuit design. In the second proposed technique, thermal noise sampled on an input capacitor is actively canceled using an amplifier, so that the noise at the amplifier output can be controlled independently of input capacitor size. Measurements from two test chips are presented which demonstrate sampled thermal noise power reduction of 48% and 67%, respectively, when compared with conventional kT/C-limited sampling.