AD210 low side of the signal source. This will not work if the source has CHANNEL OUTPUTS another current path to input common or if current flows in the 123 signal source LO lead. To minimize CMR degradation, keep the resistor in series with the input LO below a few hundred ohms. Figure 5 also shows the preferred gain adjustment circuit. The circuit shows RF of 50 kΩ, and will work for gains of ten or greater. The adjustment becomes less effective at lower gains (its effect is halved at G = 2) so that the pot will have to be a larger fraction of the total R 0.1" F at low gain. At G = 1 (follower) GRID the gain cannot be adjusted downward without compromising input impedance; it is better to adjust gain at the signal source POWER or after the output. Figure 6 shows the input adjustment circuit for use when the input amplifier is configured in the inverting mode. The offset adjustment nulls the voltage at the summing node. This is pref- erable to current injection because it is less affected by subse- quent gain adjustment. Gain adjustment is made in the feedback and will work for gains from 1 V/V to 100 V/V. GAIN47.5k Ω RRRRRR16GFGFGF5k Ω VOUT123171CHANNEL INPUTSRS19 Figure 8. PCB Layout for Multichannel Applications with 200 Ω AD210VSIG Gain 182Synchronization: The AD210 is insensitive to the clock of an 50k Ω +V14ISS adjacent unit, eliminating the need to synchronize the clocks. +VOSS3100k Ω However, in rare instances channel to channel pick-up may 15–VISS–V4OSS occur if input signal wires are bundled together. If this happens, OFFSET3029 shielded input cables are recommended. +15VPERFORMANCE CHARACTERISTICS Figure 6. Adjustments for Inverting Input Common-Mode Rejection: Figure 9 shows the common- Figure 7 shows how offset adjustments can be made at the out- mode rejection of the AD210 versus frequency, gain and input put, by offsetting the floating output port. In this circuit, ± 15 V source resistance. For maximum common-mode rejection of would be supplied by a separate source. The AD210’s output unwanted signals, keep the input source resistance low and care- amplifier is fixed at unity, therefore, output gain must be made fully lay out the input, avoiding excessive stray capacitance at in a subsequent stage. the input terminals. 18016G = 100160R171LO = 0G = 1V Ω OUT19140AD21050k Ω RLO = 500182 Ω 120R200 Ω LO = 0 Ω 0.1µF+V14ISS+VOSS3100CMR – dBRLO = 10k100k Ω 15–VISS–V4OSSOFFSET80RLO30= 10k29+15V–15V Ω 60+15V Figure 7. Output-Side Offset Adjustment 4010 20 50 60 100 200 500 1k 2k 5k 10kPCBLayout for Multichannel Applications: The unique FREQUENCY – Hz pinout positioning minimizes board space constraints for multi- Figure 9. Common-Mode Rejection vs. Frequency channel applications. Figure 8 shows the recommended printed circuit board layout for a noninverting input configuration with gain. –4– REV. A