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Drive Current Switching Function Added to High-Speed Low-Power CCD Image Sensor
Output Drive Buffer IC for Digital Still Cameras
CXA3741UR
In 2005, Sony developed and released the CXA3691EN high-speed
low-power CCD image sensor output drive buffer IC (“buffer IC”)
that was fabricated in Sony’s unique high-speed, high-voltage handling
complementary bipolar process. This buffer IC was highly
regarded by digital still camera designers.
To respond to desires for even higher power efficiency, Sony is
now releasing the new CXA3741UR buffer IC, which adds switching
functions for both the output drive current and input sink current.
This product achieves even higher levels of power savings
by reducing current consumption at times other than tripping shutter. |
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CXA3741UR |
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* Reduced power consumption: 24 mW*1
* Output drive current switching control
(new function)
* Input sink current switching control
(new function)
* Miniature QFN package (2.3 mm square)
*1: When used with a 15 V power supply, at room temperature,
and with 220 kΩ external resistors connected to IDRV0/1. |
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Push-Pull Drive |
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Conventionally, a discrete emitter follower
circuit such as that shown in figure 1(a)
has been used for the CCD image sensor
output buffer. Since the constant-current
value in the pull direction limits the slew
rate in this circuit, the waveform can be
degraded, and noise and distortion introduced.
(See figure 2.) To maintain the
waveform, the constant-current value, that
is, the current consumption, must be increased.
In contrast, this Sony CCD buffer IC
adopts a push-pull drive structure (figure
1(b)) and thus the drive current in both the
push and pull directions changes according
to the input waveform. As a result, the
current consumption can be held to the
absolute minimum required. This can resolve
the strong tradeoff limitation between
the length of the flexible PC board
the CCD image sensor is mounted on and
the power consumption. |
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Output Drive Current Switching
Control (new function) |
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In response to strong desires from users,
Sony added an output drive current switching
function to the CXA3741UR. This
makes even further power reductions possible
by switching the current in response
to intermittent operation or dynamic clock
rate switching.
In the CXA3691EN, the output drive current
was determined by an external resistor,
while in contrast, two external resistors
can be connected to the CXA3741UR.
(These are the external resistors connected
to the IDRV0 and IDRV1 pins shown in
figure 3.) The resistor used is selected with
the logic state input to the DRVCNT pin. |
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Input Sink Current Switching
Control (new function) |
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The CXA3691EN provides an input pin
sink current for open source output type
CCD image sensors. The CXA3741UR adds
a switching function for this input sink
current. This is controlled in a similar
manner to the output drive current switching
function. (The SFCNT pin selects between
the two resistors connected to the
ISF0 and ISF1 pins.) |
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Miniature QFN package
(2.3 mm square) |
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All of these functions are integrated in a
2.3 mm square QFN package. This is a
size that can be easily mounted along with
the peripheral components on the flexible
PC board that mounts the CCD image sensor. |
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•••• Mr. TAKEYABU ••••
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Although progress has been
steady in reducing the power requirements
in semiconductor
products for use in digital still
cameras, the CCD image sensor
buffer circuit was the last remaining
impediment to power reduction.
Thus I strongly recommend
that you try the CXA3741UR. If you
don’t need the current switching
function, I recommend the
CXA3691EN. |
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See
all articles with figures and tables.  |
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Vol.47 |
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