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Dividers for LDC500/501/LDC502 Modulation Input Rev B. Revised Oct 2012 Figure 1 Balanced divider for LDC501 modulation input There is no internal way to reduce the Modulate Circuit shown above will reduce modulate input sensitivity on the LDC500, LDC501 and LDC502. sensitivity 100x, to 0.25 mA/V for low range of This has to be done externally. LDC501 and 0.5mA/V for its high range. There is a straight forward way for the user to It is important to keep R2 and R3 matched to reduce the gain on the Modulate input, and that is to preserve the CommonMode Rejection performance build a simple voltage divider to place in series with of the LDC501. Do NOT simply connect the outer the input. The only (important) caveat is that this shell from J1 to J2. must be a BALANCED divider, otherwise the commonmode rejection performance of the Since the LDC500's modulation input impedance LDC501 will be completely ruined. is about 2k, R1 should be kept below 50 ohms to ensure gain accuracy. Figure 1 shows a sketch of a circuit that will reduce the modulate sensitivity 100fold; it is straightforward to modify it from there as needed. Stanford Research Systems www.thinksrs.com (408)744-9040 -1-