##### From Mixed Signal VLSI Wireless Design: Circuits and Systems

## 7.6 TYPES OF ANALOG-TO-DIGITAL CONVERTERS

Analog-to-digital converters are classified into one-step architectures, such as: flash, folding and interpolative topologies, and multi-step architectures, such as: Successive approximation and pipeline topologies.

### 7.6.1 Flash Analog-to-Digital Converter

The flash architecture is potentially the fastest analog-to-digital converter, because of the parallelism it employs. However, this parallelism puts a practical limit on the resolution of the flash analog-to-digital converter. For an *n*-bit analog-to-digital converter, the flash architecture employs (2 ^{ n} ?1) comparators and decoding logic. A resistive ladder consisting of 2 ^{ n} equal resistors divides the reference voltage into 2 ^{ n} equally spaced voltages as shown in Figure 7.15

Figure 7.15: Block diagram of an n-bit flash analog-to-digital converter.

The output of the comparator constitutes a thermometer code. Assume that the analog input signal * ?* _{ in} is such that:

(7.33) |

Therefore, the output of comparators *C* _{1}, *C* _{2} *, * *C* _{ i} is logic 1, while the output of comparator *C* _{ i} _{+1} *,* *C* _{ i} _{+2} *, * is logic 0. The decoding logic transfers the thermometer code which has (2 ^{ n} ?1) bits into a binary signal which has *n* bits. Table 7.1 shows the mapping between the thermometer code and the binary coded signal when *n*=3.

Thermometer code | Binary code |
---|---|

0000000 | 000 |

0000001 | 001 |

0000011 | 010 |

0000111 | 011 |

0001111 | 100 |

0011111 | 101 |

0111111 | 110 |

1111111 | 111 |

##### Products & Services

##### Topics of Interest

7.7 SIGMA-DELTA ANALOG-TO-DIGITAL CONVERTERS Sigma-Delta analog-to-digital converters are commonly used when high resolution is required, this is because of the sigma-delta modulator s ability to...

5.2 Performance Parameters of Data Converters DAC Specifications The fundamental function of a D/A converter (DAC) is to transform a digital word M in into an analog (or continuous) output signal N...

OVERVIEW In the previous two chapters, we have focused on the op amp and its design. Before considering how the op amp is used to accomplish various types of analog signal processing and analog...

5.3 Nyquist-Rate DACs Integrated Nyquist-Rate DACs Recall that for a DAC, the digital input word M in in Equation (5.1) is dimensionless, and the analog output signal N out has the same dimension as...

a.out (eh dot out) n. An object file format output by some compilers and read by related linkers and loaders. See also ELF, COFF. A/D (A-to-D) abbr. See A/D converter. A/D converter n. A hardware...