AFE Channel Input Impedance

where:

• Z_IN is input impedance in Single-ended or Differential mode
• C_IN = 2 to 8 pF ±20% depending on the gain value and mode (SE or DIFF); temperature dependency is negligible
• R_ON is typical 2 kΩ and 8 kΩ max (worst case process and high temperature)

The following formula is used to calculate input impedance:

where:

• f_S is the sampling frequency of the AFE channel
• Typ values are used to compute AFE input impedance Z_IN

  Table 1. Input Capacitance (C_IN) Values

  Gain Selection	Single-ended	Differential	Unit
  1	2	2	pF
  2	4	4
  4	8	8

  Table 2. Z_IN Input Impedance

  fS (MHz)	1	0.5	0.25	0.125	0.0625	0.03125	0.015625	0.007813
  CIN = 2 pF
  ZIN (MΩ)	0.5	1	2	4	8	16	32	64
  CIN = 4 pF
  ZIN (MΩ)	0.25	0.5	1	2	4	8	16	32
  CIN = 8 pF
  ZIN (MΩ)	0.125	0.25	0.5	1	2	4	8	16