EL2020CN 데이터 시트보기 (PDF) - Elantec -> Intersil

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EL2020CN

EL2020C / 50 MHz Current Feedback Amplifier

Elantec -> Intersil 

EL2020C

50 MHz Current Feedback Amplifier

Application Information

Theory of Operation

The EL2020 has a unity gain buffer similar to the

EL2003 from the non-inverting input to the in-

verting input The error signal of the EL2020 is a

current flowing into (or out of) the inverting in-

put A very small change in current flowing

through the inverting input will cause a large

change in the output voltage This current ampli-

fication is the transresistance (ROL) of the

EL2020 VOUT e ROL IINV Since ROL is

very large ( 106) the current flowing into the

inverting input in the steady state (non-slewing)

condition is very small

Therefore we can still use op-amp assumptions as

a first order approximation for circuit analysis

namely that

1 The voltage across the inputs 0 and

2 The current into the inputs is 0

Simplified Block Diagram of EL2020

in a lower b3 dB frequency Attenuation at high

frequency is limited by a zero in the closed loop

transfer function which results from stray capaci-

tance between the inverting input and ground

Power Supplies

The EL2020 may be operated with single or split

power supplies as low as g3V (6V total) to as

high as g18V (36V total) The slew rate degrades

significantly for supply voltages less than g5V

(10V total) but the bandwidth only changes 25%

for supplies from g3V to g18V It is not neces-

sary to use equal value split power supplies i e

b5V and a12V would be excellent for 0V to 1V

video signals Bypass capacitors from each sup-

ply pin to a ground plane are recommended The

EL2020 will not oscillate even with minimal by-

passing however the supply will ring excessively

with inadequate capacitance To eliminate supply

ringing and the errors it might cause a 4 7 mF

tantalum capacitor with short leads is recom-

mended for both supplies Inadequate supply by-

passing can also result in lower slew rate and

longer settling times

Non-Inverting Amplifier

2020 – 10

Resistor Value Selection and

Optimization

The value of the feedback resistor (and an inter-

nal capacitor) sets the AC dynamics of the

EL2020 A nominal value for the feedback resis-

tor is 1 kX which is the value used for produc-

tion testing This value guarantees stability For

a given gain the bandwidth may be increased by

decreasing the feedback resistor and conversely

the bandwidth will be decreased by increasing

the feedback resistor

Reducing the feedback resistor too much will re-

sult in overshoot and ringing and eventually os-

cillations Increasing the feedback resistor results

EL2020 Typical Non-Inverting

Amplifier Characteristics

2020 – 11

10V

AV

RF

RG Bandwidth Settling Time

1%

0 1%

a1

a2

a5

a10

820X

750X

680X

680X

None

750X

170X

76X

50 MHz

50 MHz

50 MHz

30 MHz

50 ns

50 ns

50 ns

55 ns

90 ns

100 ns

200 ns

280 ns

10

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