SAPHBCTL.
EXCBIAS
SAPHBCTL.
PGABIAS
TxBias
0
1
SAPHBCTL.
CH1EBSW
SAPHMCNF.LPBE
from ASQ
TxBias
SAPHBCTL.
PGABSW
from ASQ
RxBias
to
SDHS
SDHSCTL6.
PGA_GAIN[5:0]
from
ASQ
SAPHICTL.
MUXCTL
SAPHICTL.
MUXSEL
1
0
TxBias
RxBias
SAPHICTL.
DUMEN
ASQ_acquisition
ASQ_adc_arming
SDHS_adc_arming
SDHS_acquisition
SAPHBCTL.CPDA
Charge
Pump
en
PGA
CH1_IN
CH0_IN
Tx
Bias
0
0
1
1
from ASQ
SAPHBCTL.
ASQBSW
0
1
from ASQ
0
0
1
1
SAPHMCNF.LPBE
SAPHBCTL.
ASQBSW
SAPHBCTL.
CH0EBSW
from ASQ
0
1
from ASQ
0
0
1
1
SAPHMCNF.LPBE
SAPHBCTL.
ASQBSW
0
1
0
0
1
1
from
ASQ
SAPHMCNF.LPBE
SAPHMCNF.CPEO
SAPHMCNF.
BIMP
Rx
Bias
SAPHMCNF.
BIMP
Dummy
Input
Physical Interface (PHY) Block
506
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
Sequencer for Acquisition, Programmable Pulse Generator, and Physical
Interface (SAPH, SAPH_A)
21.3.3 Input Channels (CH0_IN and CH1_IN)
shows the functional block diagram for the input channels, CH0_IN and CH1_IN.
Figure 21-13. SAPH or SAPH_A Analog Input Signal Chain
The PGA uses only one input channel at a time, and the input channel is selected by
SAPHICTL0.MUXSEL when SAPHICTL0.MUXCTL = 0 and SAPHMCNF.LPBE = 0 (register mode) or by
the acquisition sequencer (ASQ) when SAPHICTL0.MUXCTL = 1 and SAPHMCNF.LPBE = 0 (auto
mode). Register mode uses the SAPHOCTL0, SAPHOCTL1, SAPHOSEL, and SAPHBCTL regiters to
control the signal chain. Auto mode uses the SAPHASCTL0, SAPHASCTL1, SAPHAPOL, SAPHAPLEV
and SAPHAHIZ registers to control the signal chain.
In Ultra Low Power Bias mode (SAPHMCNF=1) both register sets are and the multiplexer selection is
controlled by the ASQ.
The PGA has two input channels, but one of the channels is a dummy input, which has the same input
impedance of the real input. The dummy input is designed to meet the impedance match requirement
between transmit mode and receive mode of one channel. The dummy impedance is enabled when
SAPHICTL0.DUMEN = 1 (default).
The input multiplexer is powered by a charge pump, which generates 3.2 V from the USS LDO voltage
(1.6 V). The charge pump is turned on while the SAPHMCNF.CPEO=1 and during the preparation/arming
for SDHS acquisition. If desired, the charge pump is turned off while capturing the Rx signal through the
SDHS to reduce noise (SAPHBCTL.CPDA = 0); however, if signal capture is more than 300 µs, the
charge pump should remain on (SAPHBCTL.CPDA = 1). Configure SAPHBCTL.CPDA before starting a
measurement sequence. The clock of the charge pump is generated from a divided SDHS modulator
frequency to maintain coherence during acquisition.
The impedance of the bias voltages TxBias and RxBias can be programmed with SAPHMCNF.BIMP .This
allows to find the best fit for the reactant behavior of transducers on bias voltage changes (shorter
ringing).