MBF110
SETCUR
DCR
RAH
300 x 300
Sensor Arrays
A[3:0]
RAL
CE1
CE2
RD
SELECT
LOGIC
CAH
MUX
CAL
Temperature
Sensor
WR
8 Bit A/D
D[7:0]
DATA
BUS
BUFFER
TEST
XTAL1
XTAL2
ENCLK
OSCILLATOR
Chip Operation
The sensor array is composed of 300 rows and 300 columns of sensor
plates. Associated with each column are two sample-and-hold
circuits. A fingerprint image is sensed or captured one row at a time.
This“row capture”occurs in two phases. In the first phase, the
sensor plates of the selected row are pre-charged to the V
DD
voltage.
During this pre-charge period, an internal signal enables the first set
of sample-and-hold circuits to store the pre-charged plate voltages of
the row.
In the second phase, the row of sensor plates is discharged with a
current source. The rate at which a cell is discharged is proportional
to the“discharge current.”After a period of time (referred to as the
“discharge time”), an internal signal enables the second set of
sample-and-hold circuits to store the final plate voltages. The
difference between the pre-charged and discharged plate voltages is a
y
r
a
n
i
m
i
l
e
r
P
RSR
DTR
CONTROL LOGIC
CLK OUT
Resistance
Sensor
RSENSE
CLK
Figure 1.
MBF110 Block Diagram
measure of the capacitance of a sensor cell. After the row capture, the
cells within the row are ready to be digitized.
The sensitivity of the chip is adjusted by changing the discharge
current and discharge time. The nominal value of the current source
is controlled by an external resistor connected between the SETCUR
pin and ground. The current source is controlled from the Discharge
Current Register (DCR). The discharge time is controlled by the
Discharge Time Register (DTR).
The sensor array is a row-oriented device. Images are read out one
row at a time. The High-Order Row Address Register (RAH) and the
Low-Order Row Address Register (RAL) must be programmed to
select a row to be captured. Writing to RAL initiates a row capture.
The capture time is a function of the external clock and the DTR.
After the discharge cycle, the outputs of the row elements will be
stored in analog sample and hold circuits.
Fujitsu Microelectronics, Inc.
1
FUJITSU [ FUJITSU COMPONENT LIMITED. ]
