LM359
SNOSBT4C –MAY 1999–REVISED MARCH 2013
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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 frequency performance as illustrated in Figure 23.
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 internal amplifier parameters to suit
the requirements of a wide variety of applications in which this type of amplifier can be used.
Figure 23.
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 amplifier also facilitates DC biasing the output. The
basic operation 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 (AI) specification is the measure
of how closely these two currents match. For more details see TI Application Note AN-72 (Literature Number
SNOA666).
DC biasing of the output is accomplished by establishing a reference DC current into the (+) input, IIN(+), 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 reference current, Figure 24.
Figure 24.
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