LM359M datasheet(7/24 Pages) NSC

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Typical Performance Characteristics (Continued)

Application Hints

The LM359 consists of two wide bandwidth, decompensated

current differencing (Norton) amplifiers. Although similar in

operation to the original LM3900, design emphasis for these

amplifiers has been placed on obtaining much higher fre-

quency performance as illustrated in

Figure 1.

This significant improvement in frequency response is the

result of using a common-emitter/common-base (cascode)

gain stage which is typical in many discrete and integrated

video and RF circuit designs. Another versatile aspect of

these amplifiers is the ability to externally program many in-

ternal amplifier parameters to suit the requirements of a wide

variety of applications in which this type of amplifier can be

used.

DC BIASING

The LM359 is intended for single supply voltage operation

which requires DC biasing of the output. The current mirror

circuitry which provides the non-inverting input for the ampli-

fier also facilitates DC biasing the output. The basic opera-

tion of this current mirror is that

the current (both DC and AC)

flowing into the non-inverting input will force an equal

amount of current to flow into the inverting input . The mirror

gain (A

I) specification is the measure of how closely these

two currents match. For more details see National Applica-

tion Note AN-72.

DC biasing of the output is accomplished by establishing a

reference DC current into the (+) input, I

IN(+), and requiring

the output to provide the (−) input current. This forces the

output DC level to be whatever value necessary (within the

output voltage swing of the amplifier) to provide this DC ref-

erence current,

Figure 2.

The DC input voltage at each input is a transistor V

(

≅ 0.6 V

DC) and must be considered for DC biasing. For

most applications, the supply voltage, V

+, is suitable and

convenient for establishing I

IN(+). The inverting input bias

current, I

b(−), is a direct function of the programmable input

stage current (see current programmability section) and to

obtain predictable output DC biasing set I

IN(+) ≥ 10Ib(−).

Amplifier to Amplifier

Coupling (Input Referred)

DS007788-57

Noise Voltage

DS007788-58

Maximum Power Dissipation

DS007788-59

Note: Shaded area refers to LM359J/LM359N

DS007788-6

FIGURE 1.

DS007788-7

FIGURE 2.

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