ATM can support various services in a universal format. The transport of CBR services is an important feature of ATM

and is referred to as circnit emulation .The recovery of soaree clock hequency is one of the critical issues due to packet oriented technology. There are two classes of generic approaches to ATM timing recovery

namely

non-syncbonous methods and syncbonous methods. SFET

TS and SRTS are three main synchronous methods

among them SRTh has been accepted by ITU-T as the timing recovery standard for AALl.However it will introduce up to lUI waiting time jitter at some values of souree clock frequency. An improvement method

namely Synchronous Filtered Residual Time Stamp（SFRTh）

is proposed in this paper. It is based on 2-stage Sigma-Delta quantization and reduces the waiting time jitter below 0.02UI so that it greaily improves timing quality in ATM.