I highly recommend this book to learn VHDL " circuit design with VHDL, by Volnei A. Pedroni". I started learning VHDL two weeks ago and I'm using this book I think it is a great text book with plenty of examples.
Good luck
1. CMOS Analog Circuit Design
Allen & Holberg
HRW
0-03-006587-9
2.Analog Circuit Design: Mixed A/D Circuit Design, Sensor Interface Circuits, and C
ommunication Circuits Sansen,
Huijsing, van de Plassche (editors)
KAP
0-7923-9408-9
For IC design (analog and digital) I recommend "CMOS - Circuit Design, Layout and Simulation" second edition by R.Jacob Baker
It is excellently pitched at postgraduate/working engineer level. Examples and solutions provided are very relevant to Course work and real world problems.
For Sigma Delta ADC booksI recommend "Delta-Sigma Modulators - Modeling, Design and Applications"George I Bourdopoulos
"Systematic Design of CMOS Switched-Current BP Σ-Δ Modulators for Digital Communication Chips"José M. de la Rosa
"Understanding Delta-Sigma Data Converters"R Schreier
"Delta-Sigma Data Converters"S R.Norsworthy