ISL59830IA-T7 데이터 시트보기 (PDF) - Renesas Electronics

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ISL59830IA-T7

True Single Supply Video Driver

Renesas Electronics 

ISL59830

IN+

IN-

BIAS

OUT

FIGURE 27.

Description of Operation and Application

Information

Theory Of Operation

The ISL59830 is a highly practical and robust marriage of three

high bandwidth, high speed, low power, rail-to-rail voltage

feedback amplifiers with a charge pump, to provide a negative

rail without an additional power supply. Designed to operate

with a single supply voltage range of from 0V to 3.3V, the

ISL59830 eliminates the need for a split supply with the

incorporation of a charge pump capable of generating a bottom

rail as much as 1.6V below ground; for a 4.9V range on a

single 3.3V supply. This performance is ideal for NTSC video

with its negative-going sync pulses.

The Amplifier

The ISL59830 fabricated on a dielectrically isolated high speed

5V Bi-CMOS process with 4GHz PNPs and NPN transistor

exceeding 20GHz - perfect for low distortion, low power

demand and high frequency circuits. While the ISL59830

utilizes somewhat standard voltage mode feedback topologies,

there are many non-standard analog features providing its

outstanding bandwidth, rail-to-rail operation, and output drive

capabilities. The input signal initially passes through a folded

cascode, a topology providing enhanced frequency response

essentially by fixing the base collector voltage at the junction of

the input and gain stage. The collector of each input device

looks directly into an emitter that is tied closely to ground

through a resistor and biased with a very stable DC source.

Since the voltage of this collector is "locked stable" the

effective bandwidth limiting of the Miller capacitance is greatly

reduced. The signal is then passed through a second fully-

realized differential gain stage and finally through a proprietary

common emitter output stage for improved rail-to-rail output

performance. The result is a highly-stable, low distortion, low

power, and high frequency amplifier capable of driving

moderately capacitive loads with near rail-to-rail performance.

Input Output Range

The three amplifier channels have an input common mode

voltage range from 0.15V below the bottom rail to within

100mV of the positive supply, VS+ pin (Note: bottom rail is

established by the charge pump at negative one half the

positive supply). As the input signal moves outside the

specified range, the output signal will exhibit increasingly

higher levels of harmonic distortion. And of course, as load

resistance becomes lower, the current drive capability of the

device will be challenged and its ability to drive close to each

rail is reduced. For instance, with a load resistance of 1k the

output swing is within a 100mV of the rails, while a load

resistance of 150 limits the output swing to within around

300mV of the rails.

Amplifier Output Impedance

To achieve near rail-to-rail performance, the output stage of the

ISL59830 uses transistors in the common emitter

configuration, typically producing higher output impedance

than the standard emitter follower output stage. The

exceptionally high open loop gain of the ISL59830 and local

feedback reduces output impedance to less than a 2 at low

frequency. However, since output impedance of the device is

exponentially modulated by the magnitude of the open loop

gain, output impedance increases with frequency as the open

loop gain decreases with frequency. This inductive-like effect of

the output impedance is countered in the ISL59830 with

proprietary output stage topology, keeping the output

impedance low over a wide frequency range and making it

possible to easily and effectively drive relatively heavy

capacitive loads.(See Figure 11).

FN7489 Rev.1.00

May 4, 2006

Page 11 of 15

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