LM359 datasheet(11/24 Pages) NSC

11 / 24 page

Application Hints (Continued)

Determine maximum value for R

f to provide stable DC

biasing

Optimum output DC level for maximum symmetrical swing

without clipping is:

f(MAX) can now be found:

This value should not be exceeded for predictable DC bias-

ing.

Select R

s to be large enough so as not to appreciably

load the input termination resistance:

s ≥ 750Ω; Let Rs = 750Ω

Select R

f for appropriate gain:

7.5 k

Ω is less than the calculated R

f(MAX) so DC predictability

is insured.

Since R

f = 7.5k, for the output to be biased to 5.1 VDC,

the reference current I

IN(+) must be:

Now R

b can be found by:

Select C

i to provide the proper gain for the 8 Hz mini-

mum input frequency:

A larger value of C

i will allow a flat frequency response down

to 8 Hz and a 0.01 µF ceramic capacitor in parallel with C

will maintain high frequency gain accuracy.

Test for peaking of the frequency response and add a

feedback “lead” capacitor to compensate if necessary.

A NON-INVERTING VIDEO AMPLIFIER

For this case several design considerations must be dealt

with.

•

The output voltage (AC and DC) is strictly a function of

the size of the feedback resistor and the sum of AC and

DC “mirror current” flowing into the (+) input.

•

The amplifier always has 100% current feedback so ex-

ternal compensation is required. Add a small (1 pF–5 pF)

feedback capacitance to leave the amplifier’s open loop

response and slew rate unaffected.

•

To prevent saturating the mirror stage the total AC and

DC current flowing into the amplifier’s (+) input should be

less than 2 mA.

•

The output’s maximum negative swing is one diode

above ground due to the V

BE diode clamp at the (−) input.

Final Circuit Using Standard 5%

Tolerance Resistor Values:

DS007788-18

Circuit Performance:

DS007788-19

Vo(DC) = 5.1V

Differential phase error < 1˚ for 3.58 MHz fIN

Differential gain error < 0.5% for 3.58 MHz fIN

f−3 dB low = 2.5 Hz

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