Errors of "single channel quantized" correlators are analysed. The total error due to finite observation and bias is dependent on the limited level of the quantized input signal.It is pointed out that there is an optimum limited level range within which the total error should be minimized and the minimum error is almost independent of the quantized number. However

the optimum limited level range is dependent on the quantized number. Taking advantage of the analysis of the bias

an unbiased correlator without multiplier is deduced for Gaussian process and sinusoidal wave with random phase. According to the error analysis of this correlator

it is concluded that the correlator without multiplier is rather simple and accurate and therefore is especially suitable for high frequency measurements.