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I have 4 very high-impedance analog signals coming from a fine-pitch 100-pin connector to AD8244 buffer inputs. An electrochemical biosensor IC will be mouted on this connector. Its reference elect...
#2: Post edited
by
newbie
·
2026-04-24T19:47:01Z (5 months ago)
- I have 4 very high-impedance analog signals coming from a [fine-pitch 100-pin connector](https://suddendocs.samtec.com/prints/seam8-xx-sxx.x-xxx-xx-x-xx-x-xx-mkt.pdf) to [AD8244 buffer ](https://www.analog.com/media/en/technical-documentation/data-sheets/ad8244.pdf)inputs. An electrochemical biosensor IC will be mouted on this connector. Its reference electrode pin is connected to buffer. The buffer output is connectes to AD5941. The board stack-up is:
- Signal
- GND
- PWR + GND
- Signal
- After the AD8244, the buffer outputs go to an AD5941, so my concern is only the connector-to-AD8244 input section, which is the high-impedance part.
- The SEAX8 leads have an alternating pitch of 1.20mm and 0.80mm between pairs (not a pure uniform 0.80mm grid like a BGA).
- **[FOOTPRINT:](https://www.samtec.com/products/seam8-10-s02.0-s-10-3)**
- 
- From the AD8244 datasheet, guarding seems recommended for very high-impedance input nodes. My practical problem is that the connector escape area is very dense, so it may be difficult to place proper guard traces immediately from the connector pins.
I would like to ask:- Is it acceptable to start guarding only after the connector breakout, and focus mainly near the AD8244 input pins?
- If there is a short unguarded section in the connector fanout, is that usually acceptable if the rest of the route is done carefully?
- Since I already have a GND plane in the stack-up, does that reduce the need for guarding, or is a true driven guard still necessary for this kind of node?
- If guard traces are used, do they need to be present on all 4 layers, or only on the layer where the high-impedance signal is actually routed?
- If full guarding is not practical near the connector, what is the next best approach?
- keep the traces short
- keep them away from digital lines
- use GND shielding where driven guard is not possible
- I have 4 very high-impedance analog signals coming from a [fine-pitch 100-pin connector](https://suddendocs.samtec.com/prints/seam8-xx-sxx.x-xxx-xx-x-xx-x-xx-mkt.pdf) to [AD8244 buffer ](https://www.analog.com/media/en/technical-documentation/data-sheets/ad8244.pdf)inputs. An electrochemical biosensor IC will be mouted on this connector. Its reference electrode pin is connected to buffer. The buffer output is connectes to AD5941. The board stack-up is:
- Signal
- GND
- PWR + GND
- Signal
- After the AD8244, the buffer outputs go to an AD5941, so my concern is only the connector-to-AD8244 input section, which is the high-impedance part.
- The SEAX8 leads have an alternating pitch of 1.20mm and 0.80mm between pairs (not a pure uniform 0.80mm grid like a BGA).
- **[FOOTPRINT:](https://www.samtec.com/products/seam8-10-s02.0-s-10-3)**
- 
- From the AD8244 datasheet, guarding seems recommended for very high-impedance input nodes. My practical problem is that the connector escape area is very dense, so it may be difficult to place proper guard traces immediately from the connector pins.
- **I would like to ask:**
- Is it acceptable to start guarding only after the connector breakout, and focus mainly near the AD8244 input pins?
- If there is a short unguarded section in the connector fanout, is that usually acceptable if the rest of the route is done carefully?
- Since I already have a GND plane in the stack-up, does that reduce the need for guarding, or is a true driven guard still necessary for this kind of node?
- If guard traces are used, do they need to be present on all 4 layers, or only on the layer where the high-impedance signal is actually routed?
- If full guarding is not practical near the connector, what is the next best approach?
- keep the traces short
- keep them away from digital lines
- use GND shielding where driven guard is not possible
#1: Initial revision
by
newbie
·
2026-04-24T19:46:22Z (5 months ago)
Guarding high-impedance AD8244 input traces from a fine-pitch connector — how much is really needed?
I have 4 very high-impedance analog signals coming from a [fine-pitch 100-pin connector](https://suddendocs.samtec.com/prints/seam8-xx-sxx.x-xxx-xx-x-xx-x-xx-mkt.pdf) to [AD8244 buffer ](https://www.analog.com/media/en/technical-documentation/data-sheets/ad8244.pdf)inputs. An electrochemical biosensor IC will be mouted on this connector. Its reference electrode pin is connected to buffer. The buffer output is connectes to AD5941. The board stack-up is: Signal GND PWR + GND Signal After the AD8244, the buffer outputs go to an AD5941, so my concern is only the connector-to-AD8244 input section, which is the high-impedance part. The SEAX8 leads have an alternating pitch of 1.20mm and 0.80mm between pairs (not a pure uniform 0.80mm grid like a BGA). **[FOOTPRINT:](https://www.samtec.com/products/seam8-10-s02.0-s-10-3)**  From the AD8244 datasheet, guarding seems recommended for very high-impedance input nodes. My practical problem is that the connector escape area is very dense, so it may be difficult to place proper guard traces immediately from the connector pins. I would like to ask: Is it acceptable to start guarding only after the connector breakout, and focus mainly near the AD8244 input pins? If there is a short unguarded section in the connector fanout, is that usually acceptable if the rest of the route is done carefully? Since I already have a GND plane in the stack-up, does that reduce the need for guarding, or is a true driven guard still necessary for this kind of node? If guard traces are used, do they need to be present on all 4 layers, or only on the layer where the high-impedance signal is actually routed? If full guarding is not practical near the connector, what is the next best approach? keep the traces short keep them away from digital lines use GND shielding where driven guard is not possible