| 摘要 |
<p>PURPOSE:To enable accurate measurement based on a stable reference voltage level by providing a clamp circuit between an A/D converter and an amplifier to always keep a DC level of a Raman scattered light signal at a fixed value. CONSTITUTION:An input signal is added to an output voltage of an error amplifier 18 and the results are applied to an A/D converter 5 while being inputted into an LPF 15. Here, noise of the signal is governed by that due to a Raman scattered light component and an S/N ratio is relatively satisfactory in a non- signal area. But the noise in this area is cut with the LPF 15 to upgrade a clamping performance. Then, the signal is sampled and held at a timing of a clamp pulse and a voltage in the non-signal area of the signal is compared with a level of a reference voltage 17. An error obtained is amplified and added up to the input signal to form a feedback group. Thus, the non-signal area of the Raman scattered light signal inputted into the A/D converter 5 can be kept constant being equal to the reference voltage.</p> |
