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Rev. 1.20
59
October 28, 2020
BC45B4523
ADC_FullScaleAdj
[1:0]
Effective RF Input Amplitude (mVp) Step Size
ADC_Rsln=0 (7 bits)
ADC_Rsln=1 (8 bits)
00
10.6mVp
5.3mVp
01
8.0mVp
4.0mVp
10
13.1mVp
6.6mVp
11
15.9mVp
7.9mVp
Effective RF Input Amplitude Step Size for ADC_FullScaleAdj and ADC_Rsln at RX Pin
The following figure shows the basic operation in CardDetect mode. After CardDetect command is executed,
the device will automatically disable transmitter by clearing TX_EN to 0. Then ADC and VREF circuit will be
enabled by ADC_EN signal. The ADC_Delay bit field (Sector0-0x25.[5:4]) are used to configure delay time for
analog signal settle before transmitter is re-enabled. After transmitter is turned on, ADC will wait for a short time
setting by CDTxDelay bit (Sector0-0x31.2) for RF signal settle before start conversion by setting ADC_Convert
to 1. The conversion period splits into 2 phases. First is the “sense” phase, in which transmitter drives RF field
and ADC monitors RF amplitude changing when card or tag is loaded into field. The other is “process”, in which
transmitter is turned off and ADC data is calculated. After the conversion is completed, IdleIRq is set. And if the
value of register ADC_Result_I (Sector0-0x26) or ADC_Result_Q (Sector0-0x27) are beyond threshold level,
CDIRq will be set. The following table shows the conversion time for each configuration.
N/A
ADC_EN
ADC_Convert
TX_EN
CDTxDelay
RX
ADC_Delay
Conversion
VMID
level
CardDetect Mode
Sense
Process
ADC_Result
IdleIRq
CDIRq
Basic Timing for CardDetect Mode
ADC_FastMode ADC_Rsln
Sense Period
(T_sense)
Max Conversion Time
(“T_sense” + “T_process”)
0
0 - 7bits
4.72μs
14.12μs
1 - 8bits
4.72μs
23.60μs
1
X - 8bits
9.44μs
28.32μs
Note: T_process defined timing in “process” is varied with RF input amplitude.
ADC Conversion Time for ADC_FastMode and ADC_Rsln Configurations
For FieldDetect operation, the basic timing is quite similar to CardDetect operation. The timing is shown in the
following figure. The different point is that in “sense” period, transmitter is still disabled to sense external RF field.
When operation is completed, IdleIRq is set. And if the value of register ADC_Result_I (Sector0-0x26) or ADC_
Result_Q (Sector0-0x27) are beyond threshold level, RxIRq will be set.