Recently, speedup in data communication is progressing in a large variety of electronic devices, such as server network devices, mobile phones, storage devices, OA devices or domestic electrical or electronic utensils. In addition, a high-speed operation is preferred in data communication among different ones of the electronic devices. In signal transmission in such high-speed communication, severe signal distortion is liable to occur due to inter-symbol interference, sometimes abbreviated to ISI below, or due to noise. Thus, an equalizing technique to correct the signal waveform has been a desideratum. Inter alia, the decision feedback equalizer, sometimes abbreviated to DFE below, may be used to good effect to remove the ISI, and is now in use in e.g., the wireless signal receiving technique (see Patent Literature 1).
FIG. 10 depicts a block diagram showing the configuration of a customary decision feedback equalizer disclosed in e.g., Patent Literature 1. The decision feedback equalizer includes an adder 121, a decision circuit 111, a plurality of latch circuits L12 to L1n, n being an integer not less than 2, a plurality of coefficient units Tap11 to Tap1n, and an output amplifier 132. The adder 121 adds a feedback signal to a received signal, entered thereto via an input amplifier 131, or subtracts the feedback signal from the received signal. The decision circuit 111 decides an output addition signal of the adder 121 to be “1” or “0”, and the latch circuits L12 to L1n are connected together in cascade to sequentially shift the results of the decision. The coefficient units Tap11 to Tap1n operate to multiply the outputs of the decision circuit 111 and the latch circuits L12 to L1n with weighting coefficients (tap coefficients), and the output amplifier 132 outputs the results of the decision of the decision circuit 111 to outside. The adder 121 receives outputs of the coefficient units Tap11 to Tap1n as feedback signals.
The above described decision feedback equalizer uses a multi-tap configuration that applies a plurality of feedback processing operations to signals preceding the current signal by one, two, three, . . . , n periods to remove the signal interference by retrogressing not only to the directly previous signal but also to the multiple previous signals. Note that the signal interference previous to the current signal by k periods, where k is 1 to n, is termed kth-post.
Among the methods for setting tap coefficients of respective feedback paths, there are a method of setting fixed values, decided from the outset depending on transmission characteristics, and a method of adaptively controlling the coefficient units to reduce as much as possible an error signal ε of an error detector 114 that compares input and output signals of the decision circuit 111. Any of these methods may be used to realize proper waveform equalization.
JP Patent Kokai JP-A-6-204902