UG-1262
Rev. B | Page 102 of 312
HIGH SPEED TIA CIRCUITS
The high speed TIA is intended for measuring wide bandwidth input signals up to 200 kHz. The output of the high speed TIA transfers
to the main ADC mux, where the high speed TIA can be selected as the ADC input channel. The high speed TIA is especially designed
for impedance measurements in conjunction with the high speed DAC and excitation amplifier. To connect the high speed TIA to the
external sensor pins, the user must configure the Tx switches as described in the Tx Switches section.
KEY FEATURES
To turn on the high speed TIA, set AFECON, Bit 11 = 1. Clear to 0 to power down the high speed TIA. The high speed TIA is off by
default.
The high speed TIA has programmable flexibility built into its input signal selection, R
TIA
selection, R
LOAD
selection, and common-mode
voltage source. The input signal options are as follows:
SE0 input pin from sense electrode of Channel 0 sensor.
SE1 input pin from sense electrode of Channel 1 sensor.
AIN0, AIN1, AIN2, and AIN3/BUF_VREF1V8 input pins.
DE0 input pin. This is the Diagnostic Electrode 0 pin (DE0). This pin has its own R
LOAD03
and R
TIA2_03
options configurable via the
DE0RESCON register.
DE1 input pin. This is the Diagnostic Electrode 1 pin (DE1). This pin has its own R
LOAD05
and R
TIA2_05
options configurable via the
DE1RESCON register.
The R
TIA2_x
options are in the 50 Ω to 160.1 kΩ range for the DE0 and DE1 inputs. For all other pins, the gain range is 200 Ω to 160 kΩ.
The R
LOADx
option for the SE0 and SE1 channels is a fixed 100 Ω resistor. However, for the DE0 and DE1 input pins, the R
LOADx
is
programmable. The R
LOADx
values are 0 Ω, 10 Ω, 30 Ω, 50 Ω, and 100 Ω.
Table 120. Configuration of R
LOAD
and R
TIA
of High Speed TIA When Using DE0 and DE1 Electrodes
DE0RESCON, Bits[7:0] (DE0) and DE1RESCON, Bits[7:0] (DE1) Setting
R
LOAD03
and R
LOAD05
Value (Ω)
R
TIA2_03
and R
TIA2_05
Value
0xFF Disconnected
Disconnected
0x00 0
50
Ω
0x18 0
100
Ω
0x38 0
200
Ω
0x58
0
1.1 kΩ
0x60 0
5.1
kΩ
0x68 0
10.1
kΩ
0x70 0
20.1
kΩ
0x78 0
40.1
kΩ
0x80 0
80.1
kΩ
0x88 0
160.1
kΩ
0x9 10
50
Ω
0x21 10
100
Ω
0x39 10
190
Ω
0x59 10
1.09
Ω
0x61 10
5.09
kΩ
0x69 10
10.09
kΩ
0x71 10
20.09
kΩ
0x79 10
40.09
kΩ
0x81 10
80.09
kΩ
0x89 10
160.09
kΩ
0x12 30
50
Ω
0x2A 30
100
Ω
0x4A 30
210
Ω
0x5A 30
1.07
kΩ
0x62 30
5.07
kΩ
0x6A 30
10.07
kΩ
0x72 30
20.07
kΩ