RFM31B Datasheet, PDF (38/63 Pages) List of Unclassifed Manufacturers – ISM RECEIVER

RFM31B
8.3. General Purpose ADC
An 8-bit SAR ADC is integrated for general purpose use, as well as for digitizing the on-chip temperature sensor
reading. Registers 0Fh "ADC Configuration", 10h "Sensor Offset" and 4Fh "Amplifier Offset" can be used to
configure the ADC operation.
Every time an ADC conversion is desired, bit 7 "adcstart/adcbusy" in “Register 1Fh. Clock Recovery Gearshift
Override” must be set to 1. This is a self clearing bit that will be reset to 0 at the end of the conversion cycle of the
ADC. The conversion time for the ADC is 350 µs. After this time or when the "adcstart/adcbusy" bit is cleared, then
the ADC value may be read out of register 11h "ADC Value".
The architecture of the ADC is shown in Figure 19. The signal and reference inputs of the ADC are selected by
adcsel[2:0] and adcref[1:0] in “Register 0Fh. ADC Configuration,” respectively. The default setting is to read out the
temperature sensor using the bandgap voltage (VBG) as reference. With the VBG reference the input range of the
ADC is from 0–1.02 V with an LSB resolution of 4 mV (1.02/255). Changing the ADC reference will change the LSB
resolution accordingly.
A differential multiplexer and amplifier are provided for interfacing external bridge sensors. The gain of the amplifier
is selectable by adcgain[1:0] in Register 0Fh. The majority of sensor bridges have supply voltage (VDD) dependent
gain and offset. The reference voltage of the ADC can be changed to either V_DD/2 or V_DD/3. A programmable V_DD
dependent offset voltage can be added using soffs[3:0] in register 10h.
See “General Purpose ADC Configuration” for mo re details on the usage of the general purpose ADC.
Diff. MUX
Diff. Amp.
GPIO0
GPIO1
GPIO2
adcsel [2:0]
Temperature Sensor
aoffs [4:0] soffs [3:0]
adcgain [1:0]
Input MUX
V_DD / 3
V_DD / 2
V_BG (1.2V)
adcsel [2:0]
Ref MUX
8-bit ADC
V_in
V_ref
0 -1020mV / 0-255
adc [7:0]
adcref [1:0]
Figure 19. General Purpose ADC Architecture
Add R/W
0F R/W
Function/Description
ADC Configuration
D7
D6
D5
D4
D3
D2
D1
D0 POR Def.
adcstart/adcbusy adcsel[2] adcsel[1] adcsel[0] adcref[1] adcref[0] adcgain[1] adcgain[0] 00h
10 R/W
Sensor Offset
soffs[3] soffs[2] soffs[1] soffs[0]
00h
11
R
ADC Value
adc[7]
adc[6] adc[5] adc[4]
adc[3]
adc[2]
adc[1]
adc[0]
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