nrf51822 ADC always reads 0.6v

[_Scott_]

I'm trying to get the ADC running on an nrf51DK, however whatever configuration I use it always outputs a value equivalent to ~0.6v input. I've tried with the basic ADC example in the sdk 12.3 examples folder, and still run into this issue. I have tried all of the input scaling configuration options, NRF_ADC_CONFIG_SCALING_INPUT_FULL_SCALE, NRF_ADC_CONFIG_SCALING_INPUT_ONE_THIRD, and NRF_ADC_CONFIG_SCALING_INPUT_TWO_THIRDS, and while the value that is output by the ADC does change, it still is equivalent to ~0.6v  based on the reference voltage. I have tried all of the reference voltage options as well, and while again the ADC value varies, it is still equivalent to 0.6v.

If I set the input to tie to the supply using NRF_ADC_CONFIG_SCALING_SUPPLY_ONE_THIRD, then the ADC does read a value equivalent to the supply voltage. So clearly the ADC is working, it's just that any of the SCALING_INPUT options I use seem to tie it to some source of 0.6v. I have connected the input pin to ground, vdd, and an external power supply, and it always reads the same value. It seems the input pin is ignored entirely in favor of some 0.6v source.

I found this dev zone post 

 ADC result not changing 

But the solution in that was to ensure the config was set to SCALING_INPUT, not a SCALING_SUPPLY option. I verified that I had not mistyped the configuration, so this solution did not help me.

Let me know what I can do to troubleshoot further, I'm at a bit of a wall seeing as I can't even get the example project to work. I tried the adc_timer_driven_scan_mode from the following examples, and still only got 0.6v as the output.

https://github.com/NordicPlayground/nrf51-ADC-examples

[_Scott_]

devzone.nordicsemi.com/.../7317.ADC_5F00_Config.pdf

So reading through this documentation, Figure 1 and the paragraph above it reveals the ADC has an internal power supply of 0.6v. It would appear what I am stuck reading is the internal power supply voltage. The ADC configuration will cause R^ain to vary by table 1. The signal generator I am using to output a dc signal has 50ohm output impedance. Accounting for 50ohms and R^ain in a voltage divider calculation, I should still not be seeing 0.6v as the Analog in value. However since I have tried every ADC configuration option, it would seem my issue stems from a circuit layout, however I am not sure how connecting a low impedance source to analog in would cause issues. The documentation linked specifically notes using less than 1kohm input impedence under the ADC Input Impedance Limitations section.