LM359 National Semiconductor, LM359 Datasheet - Page 7

• Manufacturer Part Number: LM359
• Description: Dual/ High Speed/ Programmable/ Current Mode Norton Amplifiers
• Manufacturer: National Semiconductor

Typical Performance Characteristics
Amplifier to Amplifier
Coupling (Input Referred)
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
FIGURE 1.
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7
amount of current to flow into the inverting input . The mirror
gain (A
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
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
(
most applications, the supply voltage, V
convenient for establishing I
current, I
stage current (see current programmability section) and to
obtain predictable output DC biasing set I
0.6 V
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I
) specification is the measure of how closely these
DC
b
(−), is a direct function of the programmable input
) and must be considered for DC biasing. For
Maximum Power Dissipation
Note: Shaded area refers to LM359J/LM359N
FIGURE 2.
IN
(+). The inverting input bias
IN
+
IN
(+), and requiring
, is suitable and
(+)
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10I
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b
(−).
BE