Photo IC
1 Illuminance sensors
1-1 Photo IC diodes
1-2 Light-to-frequency converter photo IC
2 Transmitter/receiver photo IC for optical link
2-1 General-purpose type
2-2 For MOST networks (150 Mbps)
CHAPTER 04
7 Applications
7-1 Simple illuminometers
7-2 High-speed digital transmission
(application example of photo IC for optical link)
7-3 LED backlight LCD display color adjustment
(application example of digital color sensor)
7-4 Multifunctional sensor for smartphones
(application example of color/proximity sensor)
7-5 Print start timing signal output for digital copiers
and laser printers
(application example of photo IC for laser beam
synchronous detection)
3 Encoder modules (displacement/rotation sensors)
4 Color sensors
4-1 Digital color sensors
4-2 I2C compatible color sensors
4-3 Color/proximity sensors
5 Light modulation photo IC (for optical switch)
6 Photo IC for laser beam synchronous detection
1
Photo IC
Photo ICs are optical devices that combine a photosensitive section and a signal processing circuit into one package. These
devices possess versatile functions according to their particular product applications. Photo ICs offer the following features
compared to devices made up of discrete parts on a circuit board.
Compact and lightweight
Resistant to electromagnetic induction noise
Ideal for mass production
High cost performance
High reliability
Photo ICs can be broadly grouped into monolithic types and hybrid types by their structures. The monolithic type contains
a photosensor and a signal processing circuit formed on the same chip. This type is extremely resistant to electromagnetic
induction noise because there is no wiring between the photosensor and signal processing circuit. In the hybrid type,
however, the photosensor and the signal processing IC are formed on separate chips and connected to each other within
one package. The hybrid type offers the advantage that specifications such as the photosensor shape and spectral response
characteristics are easy to change. When designing a photo IC to custom specifications, it is important to select the photo IC
type while seeking a balance between performance and cost.
Hamamatsu offers photo ICs that are optimized for a wide range of applications such as brightness and color sensing,
optical links using POF (plastic optical fiber), and synchronous detection for laser printers, etc. Hamamatsu has made
intensive R&D efforts over the years to create various types of opto-semiconductor processes and unique IC processes to
meet the product specifications needed by our customers. We have established a comprehensive production system ranging
from photo IC design to wafer processing, assembly, and inspection processes. We also offer our strong support system for
device analysis and evaluation including reliability testing. Feel free to consult with us about photo ICs that match your
custom specifications.
Monolithic type example
Hybrid type example
Hamamatsu Photo ICs
Application
Product name
Photo IC diode
Monolithic/hybrid
Output
Monolithic
Analog
Hybrid
Digital
Illuminance sensor
Light-to-frequency converter photo IC
Optical communication (POF)
Transmitter/receiver photo IC for optical link
(general-purpose type, for MOST network)
Monolithic
or hybrid
Displacement/rotation sensor
Encoder module
Monolithic
Color sensor
Digital color sensor, I2C compatible color sensor
Monolithic
Color, illuminance, and object sensor
Color/proximity sensor
Optical switch
Light modulation photo IC, photo IC for optical switch
Print start timing detection
in laser printer and the like
Photo IC for laser beam synchronous detection
Digital
2
Hybrid
Monolithic
Hybrid
1.
Illuminance sensors
[Figure 1-1] Block diagram
(visual-sensitive compensation type)
Photodiode for
signal detection
Photodiode for
signal compensation
1-1
Photo IC diodes
Cathode
Internal protection
resistance
(approx. 150 Ω)
Drawing surrounded
by dotted lines shows
a schematic diagram
of photo IC diode.
Reverse bias
power supply
Current amp
Anode
1
fc ≈
2πCL RL
fc: cutoff frequency
CL
Vout
RL
KPICC0163EA
Relative sensitivity (%)
[Figure 1-2] Spectral response
Photo IC diodes are monolithic ICs consisting of a
photodiode that generates electrical current from incident
light and a circuit section that amplifies the current
by several tens of thousands of times. Photo IC diodes
provide a current output and can be used in the same
way as a photodiode applied with a reverse voltage.
Photo IC diodes include visual-sensitive compensation
types and infrared types with sensitivity extending to
the near infrared range. Packages available include SIP
(single inline package), DIP (dual inline package), COB
(chip on board), and head-on types. The IC and the
package can be customized to match customer needs,
ranging from consumer electronics to in-vehicle use.
Infrared type
Visual-sensitive
compensation type
Wavelength (nm)
KPICB0084EB
Features
[Figure 1-3] Linearity (visual-sensitive compensation type)
•
Just as easy to use as photodiodes
•
Large output equivalent to phototransistors
•
Excellent linearity
(Typ. Ta=25 °C, VR=5 V, 2856 K)
10 mA
Here we describe the operating principle of visual-sensitive
compensation type photo IC diodes. The photosensitive
area of visual-sensitive compensation types is made up of a
photodiode for the main signal and a secondary photodiode
for signal compensation. An internal arithmetic circuit
subtracts the photocurrent generated in the photodiode
for signal compensation from the photocurrent generated
in the photodiode for the main signal, in order to obtain
spectral response characteristics that block out the infrared
range. The signal is then amplified by a current amplifier
and is output.
100 μA
Photocurrent
Operating principle and characteristics
1 mA
10 μA
1 μA
100 nA
10 nA
0.1
1
10
100
1000
Illuminance (lx)
KPICB0083ED
3
[Table 1-1] Electrical and optical characteristics (visual-sensitive compensation type S9648-200SB)
Parameter
Symbol
Condition
Spectral response range
λ
Peak sensitivity wavelength
λp
Dark current
ID
VR=5 V
Photocurrent
IL
Rise time
Fall time
Max.
Unit
-
300 to 820
-
nm
-
560
-
nm
1
50
nA
VR=5 V, 2856 K, 100 lx
0.18
-
0.34
mA
tr
10 to 90%, VR=7.5 V
RL=10 kΩ, λ=560 nm
-
6.0
-
ms
tf
90 to 10%, VR=7.5 V
RL=10 kΩ, λ=560 nm
-
2.5
-
ms
Apply a voltage so that a positive potential is applied to
the cathode. If the high-frequency components must be
removed, then connect a capacitive load (CL) as a lowpass filter in parallel with the load resistance (RL).
The cutoff frequency (fc) is expressed as shown in
equation (1).
•
Light-to-frequency converter photo IC
Spectral response close to human eye sensitivity
Spectral response characteristics of the photodiode used
in the light-to-frequency converter photo IC are close
to human eye sensitivity. The IC output nearly matches
human eye sensitivity because color temperature errors
are minimal.
•
High sensitivity
The photodiode in the light-to-frequency converter photo
IC is driven under conditions where the bias voltage between
the anode and cathode is near zero. This minimizes the
dark current and achieves higher sensitivity.
1
.......... (1)
2π CL RL
1-2
Typ.
-
How to use
fc ≈
Min.
•
Digital output
Output is in digital pulses so no troublesome analog
processing is required.
Operating principle and characteristics
The light-to-frequency converter photo IC is made up of a
photodiode and current-to-frequency converter. It outputs
a pulse frequency proportional to the illuminance. Output
is released during the high period of the reset pulse. The
output pulse phase is initialized when the reset pulse is
changed from high to low.
The light-to-frequency converter photo IC is a CMOS
photo IC combining a photodiode with a current-tofrequency converter. This photo IC outputs digital pulses
supporting CMOS logic, and the output frequency is
proportional to the incident light level. This photo IC can
be used in various types of light-level sensors.
[Figure 1-4] Block diagram
Vdd
Reset (out disable)
Output
Current-to-frequency
converter
Features
GND
•
Wide dynamic range
Ordinary current-to-voltage converter circuits usually
have a limited dynamic range due to the noise and
supply voltage. This light-to-frequency converter photo
IC employs a circuit that converts current directly to a
pulse frequency. So the photocurrent of the photodiode
is converted to a frequency with no loss in the wide
dynamic range. This photo IC therefore achieves a
dynamic range of five figures or more.
4
KPICC0133EB
[Figure 1-5] Spectral response
[Figure 1-8] Connection example
Relative sensitivity (%)
Light-to-frequency
converter photo IC
Light-to-frequency
converter photo IC
Microcontroller
Output
KPICC0134EB
Human eye sensitivity
Wavelength (nm)
KPICB0126EA
Output frequency (Hz)
[Figure 1-6] Output frequency vs. illuminance
Illuminance (lx)
KPICB0091EC
[Figure 1-7] Output waveform example
Illuminance 1 μW
Illuminance 0.1 μW
How to use
To detect illuminance by using the light-to-frequency converter
photo IC, find the output frequency by counting the number
of pulses in a specified period (Tg). The illuminance can also
be detected by finding the half-cycle time of the output. This
method is effective when detecting low illuminance or, in
other words, during output of a low frequency.
5
2.
Transmitter/receiver
photo IC for optical link
Optical fiber communication using plastic optical fibers
(POF) features insusceptibility to external noise, highspeed data communication capability, and the like
and is used in in-vehicle, FA, and consumer electronic
optical networks. Hamamatsu offers general-purpose
types supporting a variety of transmission speeds as well
as high-speed, high-reliability types for MOST (Media
Oriented Systems Transport) network, which is popular
in Europe.
2-1
General-purpose type
•
Wide dynamic range
Hamamatsu offers products that cover a wide range of
transmission speeds from DC to 100 Mbps. Receiver photo
ICs have a wide dynamic range (e.g., the dynamic range of
receiver photo ICs for semi high-speed communication:
-5 to -30 dBm).
Structure
Figure 2-1 shows a block diagram of the transmitter photo
IC. When an signal is input, the LED emits light. The rise
time of the optical output waveform is adjusted through
resistance and capacitance.
Figure 2-2 shows a block diagram of the receiver photo
IC. When an optical signal is input to the photodiode, an
amplifier converts the current into voltage and amplifies
the signal. Then, a comparator converts the signal into
CMOS digital output.
[Figure 2-1] Block diagram (transmitter photo IC)
Vcc
Forward current
bias circuit
Vin
Current
driver
Current
peaking circuit
Temperature
monitor
Current
source
Transmitter photo IC Receiver photo IC
GND
KPICC0200EB
We provide general-purpose optical link receiver photo
ICs that support transmission speeds from DC to 100
Mbps.
There are two types of transmitter photo ICs (with builtin LED driver circuit): one type covering DC to 10 Mbps
and another covering DC to 100 Mbps. Table 2-1 shows
the available receiver photo IC types.
[Figure 2-2] Block diagram (receiver photo IC)
Vcc
Amp
Comparator
Vout
Photodiode
Bias power supply
[Table 2-1] General-purpose receiver photo IC for optical link
GND
Type
Supply
voltage
Transmission
speed
Output
level
Low speed, high sensitivity
(for long distance communication)
DC to 1 Mbps
Low speed,
3.3 V
ultra low current consumption ±5%
CMOS
level
For semi high-speed communication
DC to 10 Mbps
For high-speed communication
DC to 100 Mbps
Features
•
Monolithic structure (receiver photo IC)
Receiver photo ICs integrate the photodiode and signal
processing circuit into a monolithic structure to reduce
effects from external electromagnetic noise. Hamamatsu
uses a unique PIN bipolar process to form the monolithic
structure. This PIN bipolar process allows manufacturing
photo ICs with high speed up to 250 Mbps.
6
KPICC0201EA
Characteristics
[Figure 2-3] Output waveforms
Features
•
(a) Optical output waveform of transmitter photo IC
(DC to 10 Mbps)
The transmitter photo IC employs a high-speed, high-power
LED with a peak emission wavelength of 650 nm. The driver
IC contains an internal temperature-compensation circuit
that suppresses optical output fluctuations caused by
changes in the ambient temperature.
•
Wide dynamic range, standby mode (receiver photo IC)
The receiver photo IC is a hybrid structure integrating
a PIN photodiode and CMOS IC, which delivers highspeed operation. It has a wide dynamic range of -2 to
-22 dBm and includes a standby function that switches
to power-saving mode when no light is input.
Horizontal axis: 40 ns/div.
PN=27 -1, 10 Mbps
•
(b) Digital output waveform of receiver photo IC for
semi high-speed communication
Uses high-speed LED (transmitter photo IC)
Full differential structure (receiver photo IC)
Receiver photo ICs employ signal processing circuit with a
full differential structure that uses a dummy photodiode
to reduce effects from power supply noise and external
electromagnetic noise. The reduction of noise effects
achieves high S/N.
Structure
Horizontal axis: 40 ns/div., vertical axis: 1 V/div.
PN=27 -1, 10 Mbps
2-2
For MOST networks
(150 Mbps)
Figure 2-4 shows a block diagram of the transmitter photo
IC. When a given electrical signal is input to the input
terminal, the RC (resonant cavity) type LED emits light. A
temperature monitor circuit senses the ambient temperature
and adjusts the LED drive current.
Figure 2-5 shows a block diagram of the receiver photo
IC. When the light level exceeding a preset level enters
the photodiode, operation shifts from standby mode to
operation mode, then the amplifier and LVDS output
circuit start operating to output an LVDS signal.
[Figure 2-4] Block diagram (transmitter photo IC)
VCC_TX
Current driver
TXP
LVDS
receiver
TXN
Peak current driver
Transmitter photo IC Receiver photo IC Transmitter/receiver photo IC
L11354-01
S11355-01
P11379-04AT
RC type
LED
Signal detection
/RST
This 150 Mbps optical link photo IC complies with the
MOST150 standard. We provide a sidelooker plastic
package type and a surface mount type that consists of
a transmitter/receiver chip in a single package with an
integrated optical fiber connector. The surface mount type
features high reliability and supports reflow soldering. We
also provide a 25 Mbps data transmission speed type.
Temperature monitor
Current source
Ctrl_TX
GND_TX
KPICC0177EA
7
[Figure 2-5] Block diagram (receiver photo IC)
VCC_RX*
[Figure 2-8] Connection example
(receiver photo IC: S11355-01)
VCC_RX2
PD
L1
+
C2
C1
+
C3
3.3 V
GND_RX
VCC_RX2
Main
amp
Preamp
Comparator
RXP
RXP
LVDS
output circuit
RXP
RXN
R1
S11355-01
RXN
GND_RX
SD
comparator
Bias
SD
judgment
STATUS
RXN
STATUS
STATUS
GND
Thick lines: 50 Ω impedance matching
KPICC0180EC
* P11379-04AT only
KPICC0178EB
Symbol
Part
R1
Resistor
L1
Inductance
Characteristics
[Figure 2-6] Output waveforms (eye pattern)
(a) Optical output waveform of transmitter photo IC
MOST stream data, 300 Mbps
(b) Digital output waveform of receiver photo IC
MOST stream data, 300 Mbps, Pin=-21.5 dBm
[Figure 2-7] Connection example
(transmitter photo IC: L11354-01)
C1
+
C2
L1
+
C3
VCC_TX
3.3 V
Ctrl_TX
Ctrl_TX
TXP
L11354-01
TXP
R1
GND_TX
/RST
TXN
TXN
/RST
GND
Thick lines: 50 Ω impedance matching
KPICC0179EB
Symbol
Part
R1
Resistor
L1
Inductance
8
C1
Capacitor
C2
C3
Capacitor
Capacitor
Constant
Remarks
100 Ω Terminator for LVDS
0.1 µH For a filter
Bypass capacitor for
0.1 µF
noise suppression
10 µF
For a filter
10 µF
For a filter
C1
Capacitor
C2
C3
Capacitor
Capacitor
Constant
Remarks
100 Ω Terminator for LVDS
0.1 µH For a filter
Bypass capacitor for
0.1 µF
noise suppression
10 µF
For a filter
10 µF
For a filter
3.
Encoder modules
(displacement/rotation sensors)
The 4-element photodiode has four photosensitive areas
which are PD1, PD2, PD3, and PD4. The photo IC output
is a 2-phase digital output (TTL compatible) consisting
of phase A and phase B. Phase A (VOA) shows which of
PD1 or PD3 is receiving more light, and phase B (VOB)
shows which of PD2 or PD4 is receiving more light.
Figure 3-4 shows changes in the signal amount that was
input to PD1 to PD4 when there was movement of the
light/dark pattern created by the slits, along with results
obtained when the electrical current from that input
signal was converted into a 2-phase digital signal via the
preamp, comparator, and output circuit.
[Figure 3-1] Block diagram and truth table
Vcc
PD1
Anode
VOA
+
-
PD2
This is an encoder module that incorporates a red LED
and a photo IC designed specifically for optical encoders.
This encoder module detects the displacement or rotation
angle of the object. When the slit optical pattern attached
to the object moves between the LED and photo IC, the
4-element photodiode in the photo IC reads the slit optical
pattern, and then outputs the pattern signals (phase A and
phase B).
PD3
PD4
VOB
+
-
Cathode
Photodiode
Preamp
LED
Hysteresis comparator
& buffer comparator
Output circuit
Output
Input
PD1
PD1
PD1
PD1
<
<
>
>
PD2
PD2
PD2
PD2
PD3
PD3
PD3
PD3
>
<
>
<
VOA
Low
Low
High
High
PD4
PD4
PD4
PD4
VOB
Low
High
Low
High
Features
[Figure 3-2] Dimensional outline (unit: mm)
Incremental type optical encoders require two LEDphotodiode pairs in order to detect the position and
direction of movement of the object. Using multiple
discrete LED-photodiode pairs has the disadvantage that
characteristics vary between components. However, this
encoder module incorporates one LED and a single-chip
4-element photodiode, so there are no problems due
to variations in characteristics between components.
Moreover, element position accuracy is high, so both
high resolution and high accuracy are ensured.
A
+0.2
5.2-0.1
+0.1
3.4-0.2
(3.2) (1.8) (3.2)
8.6-0.1
+0.2
Center of
optical axis
A block diagram of this encoder module is shown in
Figure 3-1.
A light spot emitted from the LED is transformed into
light/dark patterns via the slits and projected onto the
photosensitive area. Figure 3-3 shows recommended slit
sizes in the slit plate for this encoder module.
(2 ×) ϕ1.0
Center of slit plate
1.27 ± 0.5
1.27 ± 0.5
1.27 ± 0.5
6.8 ± 0.5
1.8 ± 0.5
2.0 ± 0.5
7.0
0.9
1.8
0.9 2.6 ± 0.3
(6 ×) 0.45
Center of
optical axis
0.7 ± 0.5
Operating principle and how to use
Reference plane
Positioning pin
(2 ×) C0.2
4.05
Small size
The encoder module uses a small package with positioning
pins.
(1.6) (2.0)
3.6 ± 0.5
(6 ×) 0.25
Hamamatsu encoder module incorporates one red LED
and one photo IC which are built into a single module
to ensure low current consumption.
•
(3.0)
2.0-0.1
Low current consumption
2.5
+0.2
(1.0)
1.6
•
Anode mark
4.5 ± 0.3
High resolution and high accuracy
KPCC0011ED
(0.5)
•
GND
Photo IC
0.8
8.6
9.4
10.2
(6 ×) C0.3
VOA
GND
Vcc
VOB
Cathode
Anode
Tolerance unless otherwise
noted: ±0.1, ±2°
Lead position is specified at
the reference plane.
Values in parentheses indicate
reference values.
KPCA0010EB
9
[Figure 3-3] Recommended slit dimensions (unit: mm, t=0.1)
(See Figure 3-2 for the center position of slit plate.)
0.2
Slit
2.0 min.
0.1
[Figure 3-5] Application circuit example
(CW/CCW pulse signal generator circuit)
KPCC0013EA
[Figure 3-4] Timing chart
Hysteresis: VT In (ER) /Rf
Multiplication factor ×1
Multiplication factor ×2
Multiplication factor ×4
KPICC0032EA
Slit movement (solid line: right direction, broken line: left direction)
KPCC0031EE
The encoder module detects the distance and direction
that the slit optical pattern moves, but it cannot detect
the absolute position of the slit optical pattern itself.
To detect the absolute position of slit optical pattern,
the origin point of the slit plate must be specified, and
the amount of movement from the origin point is then
detected. To do this, a device is needed for calculating
the encoder module’s output change count from the
origin point.
Additions to the output change count are judged as
movement farther from the origin point, while subtractions
are viewed as movement nearer the origin point. This
judgment is made by the 2-phase digital output (VOA, VOB)
making either of the following transitions.
(L, L)→(L, H)→(H, H)→(H, L)→(L, L)
(L, L)→(H, L)→(H, H)→(L, H)→(L, L)
The circuit in Figure 3-5 is a CW (forward direction)/
CCW (reverse direction) pulse signal generator circuit
that generates up-count signals and down-count signals
for counting movement distance and rotation angles.
This circuit detects the order of state transitions in VOA
and VOB at the OSC signal timing which is used as the
sampling signal, and generates pulse signals to the CWnD
terminal in response to state transitions in the forward
direction and to the CCWnD terminal in response to state
transitions in the reverse direction (CWnD/CCWnD are
output terminals for the multiplication factor × n). These
CWnD/CCWnD terminals generate “n” number of pulses
per one state transition period of VOA and VOB. This pulse
width is equal to one period of the sampling signal. Figure
3-6 shows pulse signals appearing at the output terminal
in response to state transitions of OSC, VOA, and VOB.
A suitable sampling signal frequency is 40 or more times
larger than the maximum frequency of one period of the VOA
and VOB state transitions (in Figure 3-6 this is 16 times for
[Figure 3-6] Decoder output timing chart (when used with circuit shown in Figure 3-5)
Forward direction
Reverse direction
KPICC0034EA
10
purposes of simplicity). Pulses appearing at each terminal
are generated with a slight delay from the instant that the
defined state transition occurs [maximum theoretical delay
time = 1/{2 × OSC frequency (unit: cycles)}]. Each of these
signals is input to the up-count terminal and down-count
terminal of the up/down counter. The amount of movement
from the origin point can then be detected with a circuit that
clears the up/down counter at origin position.
4.
Color sensors
4-1
Digital color sensors
This digital color sensor converts the RGB components
of light into 12-bit digital signals for output as serial data.
The digital output makes handling the data very simple.
One typical application for this digital color sensor is
adjusting the backlighting for RGB-LED back-lit liquid
crystal displays. To handle deterioration that occurs in
LED over time, the digital color sensor monitors the LED
brightness and feeds back that information to the LED
driver circuit to stabilize the color tint and brightness of
the liquid crystal display. This digital color sensor is also
widely used to make various color measurements.
Features
•
9 × 9 element photodiode
This digital color sensor is a monolithic photo IC that
integrates a photodiode and analog/digital circuits.
The photodiode consists of 9 × 9 elements arranged in
a mosaic pattern. Each element, based on the on-chip
filter, is sensitive to one of three colors which are red
(λp=610 nm), green (λp=540 nm), and blue (λp=465 nm).
The mosaic pattern of the 9 × 9 elements helps reduce
effects due to variations in brightness.
•
2-step sensitivity setting
Sensitivity can be selected from 2-step settings (highsensitivity mode and low-sensitivity mode) to measure
light over a wide illuminance range. The photosensitive
area varies depending on whether high-sensitivity or
low-sensitivity mode is used. (High-sensitivity mode
uses 9 × 9 elements, and low-sensitivity mode uses only
3 × 3 elements in the center.)
•
12-bit digital output
The light signal measured by the photodiodes is amplified
and converted into a 12-bit digital signal.
Each of the RGB photodiodes arranged in a mosaic pattern
has an internal amplifier, so the RGB components of the
incident light can be simultaneously measured with high
accuracy.
11
Characteristics
The amplifiers in this digital color sensor utilize a lightto-frequency converter. The output from the light-tofrequency converter is a square wave (digital signal), and
its frequency is proportional to the incident light level.
Outputs from each light-to-frequency converter are
counted during the high period of the Gate terminal, and
the count value is held in a register. This count value is
then serially output from the Dout terminal according to
the color in synchronization with pulses that are fed to
the CK terminal. The colors are output in the sequence
“red” → “green” → “blue,” and each color output is 12
bits.
[Figure 4-3] Spectral response
Relative sensitivity (%)
Structure and operating principle
[Figure 4-1] Block diagram
Wavelength (nm)
KPICB0089EA
Register
[Figure 4-4] Output vs. illuminance
(a) Low gain
Serial
conversion
Register
(Typ. light source A, green)
10 k
tg=100 s
Register
Timing
circuit
KPICC0110EC
Output (LSB)
1k
10 s
1s
100 ms
100
10 ms
1 ms
[Figure 4-2] Enlarged view of photosensitive area (unit: µm)
100 μs
10
132
10 μs
110
side
Pin
side
1
0.1
110
132
Pin
1
10
1k
100
10 k
100 k
1M
Illuminance (lx)
3 × 3 elements
for low-sensitivity
mode
KPICB0099EA
(b) High gain
(Typ. light source A, green)
10 k
9 × 9 elements
for high-sensitivity
mode
tg=100 s
Pin
Pin
side
Output (LSB)
1k
side
For red
For green
10 s
1s
100 ms
100
10 ms
1 ms
10
100 μs
For blue
10 μs
Note: Gaps between elements are light-shielded.
KPICC0124EA
[Table 4-1] Sensitivity setting
1
0.01
0.1
1
10
100
1k
10 k
100 k
Illuminance (lx)
KPICB0100EA
12
Gain
Mode
Effective photosensitive area
High
High sensitivity
9 × 9 elements
Low
Low sensitivity
3 × 3 elements
[Figure 4-5] Timing chart (digital color sensor)
Range
t5
t3
Gate
t4
CK
tg
12 pulses
12 pulses
····
····
t1
t2
Red output (12-bit output)
Dout
LSB
····
12 pulses
····
tck
tw
Green output (12-bit output)
····
MSB LSB
MSB
Blue output (12-bit output)
LSB
····
MSB
Operating sequence
(1) Set the Gate terminal and CK terminal to low.
(2) Select the desired sensitivity with the Range terminal.
(3) Set the Gate terminal from low to high to start integrating the light level.
(4) After the desired integration time (tg) has passed, set the Gate terminal from high to low to end the light level integration.
(5) Measurement data is output from the Dout terminal by inputting 36 CK pulses to the CK terminal.
Note 1: A total of 36 CK pulses are required to read out 3-color measurement data. Red data is output by the first 12 pulses,
green data by the next 12 pulses, and blue data by the last 12 pulses. Measurement data is output from the LSB side.
Note 2: Measurement data changes at the CK pulse rising edge.
Note 3: Do not switch the Range terminal during integration time (tg).
KPICC0115EB
How to use
The only input signals required by the digital color sensor
are a “Range” signal for setting the sensitivity, a “Gate”
signal for setting the light integration time, and a “CK”
signal for extracting the 12-bit digital data measured from
the light [Figure 4-5]. The input and output for digital
color sensors are both digital signals and so can be directly
connected to the microcontroller and easily used. The
only required external component is a bypass capacitor
(0.1 µF) that should be inserted between the power supply
and the ground.
An infrared cutoff filter is attached to the top surface
of the package of the digital color sensor to remove
infrared light. However, light from the side of the package
does not pass through the infrared cutoff filter. Some
countermeasure such as using an aperture is needed to
remove infrared light that may enter the sensor without
passing through the infrared cutoff filter.
16-bit registers are also included to measure RGB and
infrared light sequentially. The sensitivity and integration
time are adjustable so that light measurements can be
performed over a wide dynamic range.
Features
•
Supports I2C
•
Sequential measurements of RGB and infrared light
•
2-step sensitivity switching (sensitivity ratio 1:10)
•
Adjustable sensitivity (1 to 65535 times) by setting
the integration time
•
Low voltage (2.5 V, 3.3 V) operation
•
Low current consumption (75 µA typ.)
•
Small package (surface mount wafer level package)
Structure and operating principle
4-2
I2C
compatible color sensors
This color sensor incorporates an I2C interface. It is
sensitive to red (λp=615 nm), green (λp=530 nm), blue
(λp=460 nm), and infrared (λp=855 nm) light, and outputs
detected results as 16-bit digital data for each color. Four
This I2C compatible color sensor is made up of a visualsensitive compensation filter, photodiode, current-tofrequency converter, counter, timer circuit, register, I2C
interface, etc. [Figure 4-6] The photodiode consists of
4 × 10 elements arranged in a mosaic pattern [Figure
4-7], and the size of each element is 110 × 135 µm. In
ordinary color sensors, strong infrared light such as from
remote controls might cause errors in color detection.
This I2C compatible color sensor, however, prevents such
detection errors using its infrared detection function.
The colors being measured are automatically selected by
a switch, so they are sequentially measured in the order
of red, green, blue, and infrared. Furthermore, sensitivity
and integration time can be specified. The 16-bit data for
each color stored in the registers can be read out through
the I2C interface.
13
[Figure 4-6] Block diagram
4-3
Visual-sensitive
compensation filter
ADC
R
Register
16
SDA
2
I C interface
Counter
VDD
Current-to-frequency
converter
B
Color/proximity sensors
SCL
GND
Timer circuit
G IR
SDA: serial data
SCL: serial clock
KPICC0152EB
[Figure 4-7] Enlarged view of photosensitive area (unit: µm)
135
110
High gain mode
Low gain mode
For red
For green
For blue
For infrared light
KPICC0153EA
Characteristics
In low gain mode, a single-element photodiode in the
bottom center is used to measure each color. In high
gain mode, however, a 10-element photodiode is used
for each color. The gain switching sensitivity ratio is
therefore 1 to 10. Integration time (Tint) is selectable
from four preset types (184 µs, 2.88 ms, 46 ms, and 368
ms). If even higher sensitivity is needed, the integration
time can be set to a constant multiple [1 to 65535 (16 bits
or less)] of these four types of integration times.
The default is set to low-gain mode at an integration time
of 546 ms/ch (3120 times 175 µs).
The color/proximity sensor is a multifunctional sensor
that incorporates a color sensor, proximity sensor, and
3-color LED in a small package (5.5 × 1.7 × 1.0 mm). It
can be used to adjust the display image quality, perform
touchscreen on/off control, indicate incoming calls,
and so forth on smartphones and the like. Color sensors
not only detect the RGB ratios of ambient light but also
function as illuminance sensors. This feature enables
image quality to be adjusted in fine detail. In smartphone
applications, the proximity sensor detects when a face
draws near and turns off the touchscreen function and
the LCD backlight. The 3-color LED indicates incoming
calls. The red LED also functions as the proximity sensor
emitter.
Features
• I2C
interface 400 kHz, Fast mode
•
Low voltage (2.5 V, 3.3 V) operation
•
1.8 V I2C bus voltage compatible
•
Low current consumption
•
Small package: 5.5 × 1.7 × 1.0 mm
•
Supports reflow soldering
•
No need to calibrate distance inconsistencies at the
[Figure 4-8] Count value vs. illuminance (typical example)
100 k
[Initial setting (low gain, integration time 546 ms/ch), light source A]
time of shipment (30 mm ± 20%)
Red
9.48 counts/lx
Count value (counts)
10 k
1k
•
Green
7.61 counts/lx
interval can be specified through the I2C registers.
Blue
3.35 counts/lx
•
Optical synchronous detection with little effect from
background light
100
1
0.1
Structure
Infrared
1.66 counts/lx
10
(1) Color sensor
1
10
100
1k
10 k
100 k
Illuminance (lx)
KPICB0130EC
14
Proximity distance, LED driver current, and measurement
The color sensor has three channels consisting of R, G,
and B. It measures color temperature with high accuracy
and high sensitivity (from as low as 1 mlx). It has a builtin 16-bit A/D converter and continuously measures the
ratios between the three colors: red (615 nm), green (530
The proximity sensor receives the red light from the
3-color LED that is reflected from an object (e.g., face) to
detect whether the object is drawing near. For example,
in the case of smartphones, the sensor detects the
distance between the smartphone and the owner’s face
and disables the touchscreen control and turns off the
LCD backlight during a conversation in order to prevent
inadvertent operation and also to save power.
(3) 3-color LED
The 3-color LED mixes the R, G, and B colors to produce
full color. Numerous colors can be specified through
the I2C interface. In smartphones, different colors can
be assigned to incoming calls, incoming mail, incoming
SMS, and so on.
[Figure 4-9] Structure diagram
Signal processing circuit
∙ I2C interface
∙ LED driver circuit
∙ Proximity sensor circuit
∙ A/D converter
(Typ. Ta=25 °C)
100
Red
80
Green
60
Blue
40
20
0
200
400
600
800
1000
1200
Wavelength (nm)
KPICB0179EA
[Figure 4-12] Proximity distance vs. LED current
(typical example)
(Ta=25 °C, Vdd=3.3 V, white reflection plate)
100
80
When moved from far to near
60
When moved away from 0 mm
40
20
1.7 mm
Photosensitive area:
Si photodiode
∙ Color sensor
∙ Proximity sensor
[Figure 4-11] Spectral response
Relative sensitivity (%)
(2) Proximity sensor
Characteristics
Proximity distance (mm)
nm), and blue (460 nm). The sensor detects sunlight and
room light (fluorescent lamp, incandescent lamp, etc.)
and automatically adjusts with high reproducibility the
color temperature and brightness of the LCD screen.
The color sensor also functions as an illuminance sensor
to adjust the brightness of the LCD screen to a comfortable
viewing level. It detects ambient brightness in the wavelength
region where the human eye is sensitive and controls the
LCD backlight luminance accordingly in order to make the
LCD easier to view and also contribute to power savings.
5.5 mm
0
0
Emitter: 3-color LED
∙ For indicating
incoming calls
∙ For proximity sensing
20
40
60
80
100
120
LED current (mA)
KPICB0180EA
[Figure 4-10] Block diagram
VDD
A/D converter
B
Register
G
16
I2C interface
R
Counter
SDA
Current-to-frequency
converter
SCL
INT
RLED
Timer
R
IR
G
Color sensor
Proximity sensor
LED
driver
circuit
B
LED
GLED
ANODE
BLED
GND
KPICC0206EA
15
5.
Light modulation photo IC
(for optical switch)
deal with DC light input. This ensures reliable detection of
signal light even under high-illuminance DC background
light. On the other hand, high-sensitivity types (S6809,
S6846, S7136-10) allow making the detection distance
even longer.
[Figure 5-1] Block diagram and truth table
Constant voltage circuit
To each part
Buffer amp
Photodiode
Comparator
Preamp
Reference voltage
generator
Light modulation photo ICs were developed to optically
detect objects. Optical detection of objects usually uses
a photosensor/light emitter pair, like a photointerrupter
and photoreflector which detect an object when it
interrupts or reflects light. However, detection errors
might occur if fluctuating background light such as
room lighting strikes the photosensor. To prevent these
detection errors, one typical method uses optical filters
by utilizing the difference in wavelengths between
the signal light and background light. However, this
method does not work if the background light level is
too strong. Light modulation photo ICs deal with this
problem by using a synchronous detection method to
reduce detection errors and ensure a stable output even
if fluctuating background light strikes the photosensor.
This synchronous detection method pulse-modulates
the signal light and detects it in synchronization with the
modulation timing to reduce effects from “noise light”
that enters the photosensor asynchronously.
Signal processing
circuit
Oscillator
Timing signal
generator
Output
circuit
LED driver
circuit
Cathode
(LED)
Truth table
Input
Output level
Light on
Light off
KPICC0002EB
[Figure 5-2] Enlarged photo of chip and block layout
Constant
voltage circuit
Oscillator
LED driver circuit
Timing signal
generator
Comparator
Features
•
Fewer detection errors even if fluctuating background
light hits the photosensor
A typical light modulation photo IC consists of an oscillator,
a timing signal generator, an LED driver circuit, a photodiode,
a preamp, a comparator, a signal processing circuit, an
output circuit, and so on, which are all integrated on a
monolithic chip. Connecting an external LED to this photo
IC allows optical synchronous detection.
•
Output circuit
Preamp
Signal processing
circuit
Photodiode
Structure
Various types are available for handling higher background
light levels or offering higher sensitivity.
16
Buffer amp
Hamamatsu provides types usable even under higher
background light levels (10000 lx typ.), as well as high
sensitivity types (lower detection level: 0.2 µW/mm2 typ.),
and asynchronous type that does not require wiring to a
light emitter. These are supplied in various packages (DIP,
SIP, and surface mount type).
Types for higher background light level (S4282-51, S6986,
S10053) have a preamp with special measures added to
Circuit block configurations of a light modulation photo
IC are described below.
(1) Oscillator and timing signal generator
The oscillator produces a reference oscillation output
by charging and discharging the internal capacitor
with a constant current. The oscillation output is fed to
the timing signal generator, which then generates LED
drive pulses and other timing pulses for digital signal
processing.
(2) LED driver circuit
Characteristics
This circuit drives an externally connected LED using
the LED drive pulses generated by the timing signal
generator. The duty cycle is 1/16. The S4282-51, S6986,
and S10053 use a constant current drive, while the S6809,
S6846, and S7136-10 use an open collector drive.
[Figure 5-4] Spectral response (typical example)
(a) S4282-51, S6986, S10053
Photocurrent generated in the photodiode is converted
to a voltage via the preamp. The preamp in the S4282-51,
S6986, and S10053, which are usable at high background
light levels, uses an AC amplifier circuit shown in
Figure 5-3 to expand the dynamic range versus DC or
low-frequency fluctuating background light without
impairing signal detection sensitivity.
Relative sensitivity (%)
(3) Photodiode and preamp
[Figure 5-3] Preamp block diagram (S4282-51, S6986, S10053)
Rf1
Rf2
Wavelength (nm)
Area S1
Photodiode 1
Cc
A1
Ri2
KPICB0001EB
A2
(b) S6809, S6846, S7136-10
Rc
Buffer amp
Cf
Rf1'
A1
KPICC0025EC
(4) Capacitive coupling, buffer amp, and reference
voltage generator
Relative sensitivity (%)
Area S2
Photodiode 2
Capacitive coupling removes low-frequency background
light and also cancels the DC offset in the preamp
simultaneously. The buffer amp amplifies the signal up to
the comparator level, and the reference voltage generator
generates a comparator level signal.
The comparator has a hysteresis function that prevents
chattering caused by small fluctuations in the incident
light.
(6) Signal processing circuit
The signal processing circuit consists of a gate circuit and
a digital integration circuit. The gate circuit discriminates
the comparator output to prevent possible detection errors
caused by asynchronous background light. Background
light that enters at the same timing as the signal detection
cannot be eliminated by the gate circuit. The digital
integration circuit in a subsequent stage cancels out this
background light.
(7) Output circuit
This circuit serves as an output buffer for the signal
processing circuit and outputs the signal to an external
circuit.
KPICB0002EA
[Figure 5-5] Sensitivity temperature characteristics
(typical example)
(a) When used with Hamamatsu LED (λp=890 nm)
LED threshold forward current (relative value*)
(5) Comparator
Wavelength (nm)
(* Value at 25 °C is 1.)
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
-40
-20
0
20
40
60
80
Ambient temperature (°C)
KPICB0018EB
17
(b) Light modulation photo IC only
(λ=890 nm, * Value at 25 °C is 1.)
2
Threshold illuminance (relative value*)
[Figure 5-6] LED drive current enhancing method
(a) All types
+V
IF =
1
V - VCE (sat) - VF
R
R
LED
0
-40
-20
0
20
40
60
(b) S4282-51, S6986, S10053
80
+V
Ambient temperature (°C)
RE
KPICB0019EA
How to use
Optical synchronous detection type photoreflectors and
photointerrupters can be easily made by connecting
an infrared LED to a light modulation photo IC, which
are less affected by fluctuating background light. The
light modulation photo IC is used in reflection type
sensors that detect an object or proximity to an object by
detecting the infrared LED light reflected from the object;
and also used in transmission type sensors that detect
an object or a passing object by detecting whether the
infrared LED light beam is interrupted by the object.
An infrared LED must be connected to the light modulation
photo IC in order to perform synchronous detection. In
some applications, however, connecting an LED may not be
possible. In those cases, asynchronous type photo ICs are
used. Asynchronous photo ICs cannot remove fluctuating
background light as efficiently as the synchronous type,
but they offer the advantage that they can be used without
connecting to an infrared LED.
18
VF
IF =
VBE(ON)
RE
LED
(c) S6809, S6846, S7136-10
+V
RE
IF =
VBE(ON)
RE
LED
KPICC0028EB
(1) LED drive current enhancement
(2) Sensitivity adjustment
Detecting light over longer distances requires enhancing
the LED drive current. This means that an external driver
circuit must be added. Figure 5-6 shows simple external
circuits using a PNP transistor to enhance the LED drive
current. Another method uses a pull-up resistor connected
to the LED terminal to convert LED drive pulses to logic
signals before inputting the signals to the external LED
driver circuit. If the photo IC and the LED drive current
operate from the same power supply line, then the supply
voltage may fluctuate due to the LED drive current and
cause erroneous operation. If this happens, take measures
to stabilize the photo IC power terminal.
There is no special terminal for adjusting the sensitivity
of light modulation photo ICs. If sensitivity must be
adjusted, then change the LED drive current. To do this,
connect a variable resistor in parallel with the LED for
the S4282-51, S6986, and S10053; and connect a variable
resistor in series with the LED for the S6809, S6846, and
S7136-10. If using an external circuit to drive the LED,
adjust the external circuit constant.
[Figure 5-7] LED drive current adjusting method
6.
(a) S4282-51, S6986, S10053
Photo IC for laser beam
synchronous detection
(b) S6809, S6846, S7136-10
This photo IC detects the print start timing such as for
laser printers. It contains a high-speed PIN photodiode
and a high-speed signal processing circuit. When the
laser beam passes over the photodiode, the photo IC
outputs a digital signal to show the laser beam timing.
Features
KPICC0030EB
•
Available in high-accuracy type (dual-element photodiode)
and general-purpose type (single-element photodiode)
•
Compatible with a wide range of input laser power
Internal current amplifiers are available in a 6 × type and
20 × type. The available supply voltage types are 3.3 V and
5 V. The dual-element photodiode type delivers a stable
output even if the ambient temperature or input laser
power fluctuates, by comparing the outputs from the two
elements. The single-element photodiode type operates
so that the output is inverted when the amplitude exceeds
the comparator voltage set inside the IC.
•
Hybrid structure
The photo IC for laser beam synchronous detection uses
a hybrid structure to make use of the features of both
photodiodes and amplifiers [Figure 6-1].
19
[Figure 6-1] Enlarged photo
(dual-element photodiode type S9684)
PD1
[Figure 6-3] Terminal waveforms (S9684)
IC
Direction of laser scan
KPICC0131EB
PD2
[Figure 6-4] Propagation delay time variation vs.
input power (S9684)
Operating principle
(Typ. Ta=25 °C, Ro=1.5 kΩ)
Figure 6-2 shows a block diagram of the S9684 dual-element
photodiode type. When PD1 and PD2 are irradiated with
a laser beam, the respective photocurrents Ipd1 and Ipd2
flow. These photocurrents are amplified by the current
amplifiers and flow as source currents Io1 and Io2 to
the Ro1 and Ro2 terminals. Gain resistors R1 and R2 are
externally connected between the Ro1, Ro2 terminals and
GND terminal, so the voltage potential of R1 and R2 rises
when the source current flows. The voltage difference
between the Ro1 and Ro2 terminals is detected by a
comparator and a signal then output [Figure 6-3].
If no laser beam is irradiated on PD1 and PD2, then
the comparator output cannot be determined just by
comparing the voltages at the Ro1 and Ro2 terminals.
The comparator output must therefore be clamped
at high level if no beam is irradiated on PD1 and PD2.
However, just applying an offset to the circuit to set a
voltage difference between the Ro1 and Ro2 terminals
will cause a shift in the output timing if the input power
fluctuates. To cope with this, a limit circuit made up of a
bias circuit and diode D is used to clamp the lower limit
of the Ro1 terminal voltage.
Propagation delay time variation indicates how stable
output timing can be obtained with respect to fluctuations
in the laser power. Dual-element photodiode types excel
in this characteristic.
[Figure 6-2] Block diagram (S9684)
Current
amplifier
Externally connected
gain resistor
R2
Externally connected
gain resistor
R1
Current
amplifier
Comparator
KPICC0108EB
20
Propagation delay time variation (ns)
120
100
80
60
40
20
0
0
100
200
300
400
500
Input power (μW)
KPICB0120EB
How to use
Connect an external gain resistor (10 kΩ max.) between
Ro1 and GND (or Vcc on some products) and also between
Ro2 and GND (or Vcc on some products) [Figure 6-2].
When a laser beam is scanned over PD1 and PD2, analog
waveforms such as shown in Figure 6-5 are observed at the
Ro1 and Ro2 terminals.
The beam is scanned from PD1 toward PD2. This allows the
steep falling edge to be used as a timing signal for output.
To ensure that the output timing is stable, the input laser
power and the gain resistance must be set so that the
analog waveform amplitudes of Ro1 and Ro2 are 2 to 3 V.
[Figure 6-5] Waveform example (S9684)
Vo
Vertical axis:
5 V/div.
Ro1
Ro2
Vertical axis:
1 V/div.
21
7.
Applications
Hamamatsu Photo ICs are widely used for many different applications.
Clock: light/dark sensing Photo IC diode, Schmitt trigger circuit photo IC
Station ticket gate: passenger sensing Light modulation photo IC
Air conditioner: light/dark sensing Photo IC diode
Vending machine: light/dark sensing Photo IC diode
Vending machine: coin detection Light modulation photo IC
Auto lighting equipment: light/dark sensing Photo IC diode
TV: light/dark and color sensing Photo IC diode, digital color sensor
Auto hand washer: hand sensing Light modulation photo IC
Boiler: flame eye Photo IC diode
22
Factories
Safety devices
Light modulation photo IC
Photo IC for optical switch
Signal transmission
Detection of product passage
Transmitter/receiver photo
IC for optical link
Light modulation photo IC
Photo IC for optical switch
Digital copiers, multifunctional digital office machines
Mirror and lens positioning
Paper size detection
Photo IC for encoder/module
Light modulation photo IC
Sorter leftover paper detection
Light modulation photo IC
Signal transmission
Transmitter/receiver photo IC for optical link
Color toner contrast detection
Digital color sensor
I2C compatible color sensor
Display backlight brightness adjustment
Photo IC diode
Laser origin point detection for writing on print drum
Photo IC for laser beam synchronous detection
Remaining paper amount detection
Light modulation photo IC
Automobiles
Steering wheel angle sensing
MOST network
Transmitter/receiver photo IC for optical link
Schmitt trigger circuit photo IC
Photo IC for encoder
Jog dial
Auto ambient light level sensing headlight
Photo IC for encoder
Photo IC diode
Touchscreen switches
LED, phototransistor
Auto anti-glare mirror: ambient light level sensing
Photo IC diode
Light-to-frequency converter photo IC
Instrument illumination control
Photo IC diode
23
7-1
[Figure 7-2] Connection example
(light-to-frequency converter photo IC)
Simple illuminometers
Light-to-frequency converter
photo IC
Application example of photo IC diode
DC
3 to 5 V
Here we show a simple illuminometer made from a photo
IC diode and a comparator. A simple illuminometer can
be made by utilizing the features of photo IC diodes (good
linearity and small variations in output current). This meter
can be turned on at a specified illuminance level as shown
in the connection example in Figure 7-1 by inputting the
voltage generated across load resistor RL into the comparison
terminals on the comparator (LM111 and the like).
Photo IC diodes with spectral response characteristics
near human eye sensitivity are used in the following
applications.
Output
KPICC0101EA
[Figure 7-3] Program example
· Energy-saving sensors on TV and other appliances
· Backlight adjustment on cell phones
· Brightness adjustment on LCD panels
· Ambient light level sensing on vehicle anti-glare mirrors
· Auto light sensors
[Figure 7-1] Connection example (photo IC diode)
Note: Drawing surrounded by dotted lines shows
a schematic diagram of photo IC diode.
KPICC0100EB
KPICC0102EA
Application example of light-to-frequency converter photo IC
7-2
This is a simple illuminometer made from a light-to-frequency
converter photo IC and a single-chip microcontroller
PIC12F675 (made by Microchip Technology Inc.). The
internal 16-bit timer of PIC12F675 is used. The light-tofrequency converter photo IC and microcontroller are
connected to the same power supply, and the photo IC
output is connected to the timer input pin (no. 2) on the
microcontroller. The illuminance level appears on the
LEDs. Figure 7-3 shows a program example. The output
appears in binary, and when the number increases by 1,
then the brightness doubles. The logarithmic display is
close to that of human eye sensitivity.
24
High-speed digital transmission
(application example of photo IC for optical link)
High-speed digital transmission has become an essential
part of digital media and equipment in recent years. Metal
cables have the problem that they require some means to
reduce external noise to ensure high transmission quality.
In contrast, plastic optical fibers (POF) are unaffected by
the noise and so are suitable for use in extremely noisy
environments. Hamamatsu offers a wide lineup of photo
ICs for optical link ranging from those for digital audio
equipment up to 6.25 Gbps. These photo ICs are utilizable
in consumer electronics, FA (factory automation), OA
(office automation) equipment, in-vehicle networks, and
home networks, etc.
The color/proximity sensor was designed for smartphones,
but it can also be used in a wide range of applications that
require object sensing and brightness and color adjustment.
[Figure 7-4] In-vehicle network (MOST)
Tuner amp
[Figure 7-6] Color/proximity sensor used in smartphones
DVD player
CD changer
GPS navigation
video display
Color/proximity sensor
Interactive
security system
Telematics
KPICC0107EA
7-3
LED backlight LCD display color
adjustment (application example
of digital color sensor)
The backlight brightness on LCD displays using RGB-LED
backlighting is usually regulated by a microcontroller. Since
the backlight deteriorates over time, the color sensor is used
to monitor the backlight level. The brightness information
is fed back to the microcontroller, which then adjusts the
backlight brightness to maintain a stable display. Digital
color sensors provide digital input/output signals that can
be directly connected to the microcontroller.
LCD panel
LED
driver circuit
Backlight
[Figure 7-5] Connection example (digital color sensor)
Controller
Digital
color sensor
KPICC0148EA
7-4
Multifunctional sensor for smartphones
(application example of color/proximity sensor)
KPICC0221EA
7-5
Print start timing signal output for
digital copiers and laser printers
(application example of photo IC for
laser beam synchronous detection)
Digital copiers and laser printers record an electrostatic
latent image on a photosensitive medium by scanning
with an intensity-modulated laser beam. In this type of
raster scanning, it is essential to synchronize the scanning
signal. To do this, a photosensor is mounted at the position
where the main scanning starts, in order to generate a
synchronization signal by utilizing the received light signal
from the photosensor.
The photo IC for laser beam synchronous detection outputs
a print start timing signal. A timing signal is then generated
when the laser beam passes the position where this photo IC
is mounted and the signal sent to the phase control circuit.
The phase control circuit then uses this timing signal to set
the timing for writing the raster information from the laser
intensity modulator circuit.
Hamamatsu offers two types of photo ICs for laser beam
synchronous detection. One is a high-precision type (dualelement photodiode) and the other is a general-purpose
type (single-element photodiode).
Smartphones contain sensors for adjusting the image quality
of the LCD display and for turning on and off the touchscreen
and LEDs for indicating incoming calls. Since the amount of
space inside a smartphone is limited, mounted components
need to be small. Hamamatsu color/proximity sensor
integrates such functions in a single small package to reduce
the amount of space used by components. This sensor
operates on low voltage (2.5 V or 3.3 V) and also have a
standby mode, minimizing its power consumption.
25
[Figure 7-7] Schematic of laser printer
Photosensitive drum
Photo IC for laser beam
synchronous detection
Laser diode
Polygon mirror
KPICC0150EC
26