A 500-MSample/s, 6-bit Nyquist-rate ADC for disk-drive read-channel applications

The analog-to-digital conversion required in most disk-drive read-channel a pplications is designed for good dynamic and noise performance over a wide- input frequency range. This paper presents a 500-MSample/s, 6-bit analog-to -digital converter (ADC) and its embedded implementation inside a disk-driv e read channel, using a 0.35-mu m CMOS double-poly (only one poly layer was used in the ADC), triple-metal process. The converter achieves better than 5 effective number of bits (ENOB) for input frequencies up to Nyquist freq uency (f(in) = f(s)/2) and sampling frequencies f(s) up to 400 MHz, It also achieves better that 5.6 ENOB for input frequencies up to f(s)/4 over proc ess, temperature, and power-supply variations. At maximum speed (f(s) = 500 MHz), the converter still achieves better than 5 ENOB for input frequencie s up to f(in) = 200 MHz. Low-frequency performance is characterized by DNL < 0.32 LSB and INL < 0.2 LSB. The converter consumes 225 mW from a 3.3-V su pply when running at 300 MHz and occupies 0.8 mm(2) of chip area.