| 摘要 |
PURPOSE:To obtain a high S/N with a low quantized accuracy by forming a quantized output into a tri-state level and spreading a DC converted error with a pulse signal so as to change over the full scale of a D/A converting circuit depending on the magnitude of the input signal level. CONSTITUTION:An input analog signal is added to an output from a pulse generator 10 at an adder 2, subtracted with a velue D/A-converting (6) an output of a quantizer Q4 sampling signals in a frequency higher than an input frequency, and the result is inputted to an integration device 3. An integrated output signal is quantized into three levels, a reference voltage VREF1 or over, a middle value between VREF1 and VREF2, and the VREF2 or below by two voltage comparators 12A, 12B of a quantizer 4 and outputted to a digital filter DF7 and the D/A converter 6. The DF7 eliminates a pulse signal spreading a DC converting error from the generator 10 and outputs a digital signal corresponding to the input analog signal. The output signal is detected by a signal amplitude detecting circuit 11 and the full scale of the D/A and the DF7 is changed over into two stages depending on the magnitude of the signal amplitude so as to improve the S/N ratio to a low input level signal. |
