992215735011 Ver la hoja de datos (PDF) - Philips Electronics

Número de pieza

componentes Descripción

Fabricante

992215735011

Frame Transfer CCD Image Sensor

Philips Electronics 

Philips Semiconductors

Frame Transfer CCD Image Sensor

Product specification

FTT1010-M

Application information

Current handling

One of the purposes of VPS is to drain the holes that are generated

during exposure of the sensor to light. Free electrons are either

transported to the VRD connection and, if excessive (from over-

exposure), free electrons are drained to VNS. No current should

flow into any VPS connection of the sensor. During high overexposure

a total current 10 to 15mA through all VPS connections together

may be expected. The PNP emitter follower in the circuit diagram

(figure 12) serves these current requirements.

VNS drains superfluous electrons as a result of overexposure. In

other words, it only sinks current. During high overexposure a total

current of 10 to 15mA through all VNS connections together may be

expected. The NPN emitter follower in the circuit diagram meets

these current requirements. The clamp circuit, consisting of the diode

and electrolytic capacitor, enables the addition of a Charge Reset

(CR) pulse on top of an otherwise stable VNS voltage. To protect the

CCD, the current resulting from this pulse should be limited. This

can be accomplished by designing a pulse generator with a rather

high output impedance.

Decoupling of DC voltages

All DC voltages (not VNS, which has additional CR pulses as

described above) should be decoupled with a 100nF decoupling

capacitor. This capacitor must be mounted as close as possible to

the sensor pin. Further noise reduction (by bandwidth limiting) is

achieved by the resistors in the connections between the sensor

and its voltage supplies. The electrons that build up the charge

packets that will reach the floating diffusions only add up to a small

current, which will flow through VRD.Therefore a large series resistor

in the VRD connection may be used.

Outputs

To limit the on-chip power dissipation, the output buffers are designed

with open source outputs. Outputs to be used should therefore be

loaded with a current source or more simply with a resistance to

GND. In order to prevent the output (which typically has an output

impedance of about 400Ω) from bandwidth limitation as a result of

capacitive loading, load the output with an emitter follower built from

a high-frequency transistor. Mount the base of this transistor as close

as possible to the sensor and keep the connection between the

emitter and the next stage short.

The CCD output buffer can easily be destroyed by ESD. By using

this emitter follower, this danger is suppressed; do NOT reintroduce

this danger by measuring directly on the output pin of the sensor

with an oscilloscope probe. Instead, measure on the output of the

emitter follower. Slew rate limitation is avoided by avoiding a too-

small quiescent current in the emitter follower; about 10mA should

do the job. The collector of the emitter follower should be decoupled

properly to suppress the Miller effect from the base-collector

capacitance.

A CCD output load resistor of 3.3kΩ typically results in a bandwidth

of 110MHz. The bandwidth can be enlarged to about 130MHz by

using a resistor of 2.2kΩ instead, which, however, also enlarges the

on-chip power dissipation.

Device protection

The output buffers of the FTT1010-M are likely to be damaged if

VPS rises above SFD or RD at any time.This danger is most realistic

during power-on or power-off of the camera. The RD voltage should

always be lower than the SFD voltage.

Never exceed the maximum output current. This may damage the

device permanently. The maximum output current should be limited

to 10mA. Be especially aware that the output buffers of these image

sensors are very sensitive to ESD damage.

Because of the fact that our CCDs are built on an n-type substrate,

we are dealing with some parasitic npn transistors. To avoid activation

of these transistors during switch-on and switch-off of the camera,

we recommend the application diagram of figure 12.

Unused sections

To reduce power consumption the following steps can be taken.

Connect unused output register pins (C1...C3, SG, OG) and unused

SFS pins to zero Volts.

More information

Detailed application information is provided in the application note

AN01 entitled ‘Camera Electronics for the mK x nK CCD Image

Sensor Family’.

1999 September

13

Share Link: