Cascade, single and multi-bit, /spl Sigma//spl Delta/ architectures provide stable, high order quantization noise shaping used in high resolution A/D conversion. One major disadvantage of cascaded /spl Sigma//spl Delta/ topologies is the extreme SNDR sensitivity to gain mismatch between the analog modulator and the digital error correction logic. This paper will investigate this SNDR sensitivity phenomenon for a 6th order, 1-bit quantizer and 4th order, 5-bit quantizer cascaded /spl Sigma//spl Delta/ A/D system. Circuit parameters of the switched capacitor integrator such as amplifier open loop gain, integrator gain, and amplifier offsets and layout parasitics are characterized.

The shared-buffering architecture is promising to make a large-scale ATM switch with small buffer size. However, there are two important problems, namely, memory-access speed and complex-control implementation. Advanced 0.5 /spl mu/m CMOS technology now makes it possible to integrate a huge amount of memory, and enables us to apply more sophisticated architecture than ever before. We propose the funnel-structured expandable architecture with shared multibuffering and the advanced searchable-address queueing scheme for these two problems. The funnel structure gives a flexible capability to build various sizes of ATM switches which are proportional to the number of LSI chips. The searchable-address queue, in which all the addresses of the stored cells for different output ports are queued in a single-FIFO hardware and the earliest address is found by the search function provided inside the queue, can reduce the total memory capacity drastically, and enables the address queue to be contained inside the LSI chip. This technique also has a great advantage for implementing the multicast and multilevel priority-control functions. A 622 Mbit/s 32/spl times/8 ATM switch LSI chip set, which consists of a BX-LSI and a CX-LSI, is developed using 0.5 /spl mu/m pure CMOS technology. By using four chip sets, a 622 Mbit/s 32/spl times/32 switch can be installed on one board.

There are several schemes to provide multicast function in an ATM switch. The authors have proposed a new multicast scheme in a shared buffering ATM switch. They discuss the cell-loss performance of ATM switch to compare various schemes. Computer simulation shows that this scheme achieves the best cell-loss performance and has a great advantage in the buffer size. Implementation of an LSI chip set and a 622 Mb/s 8/spl times/8 ATM switch board is also explained.>