EL2020 Просмотр технического описания (PDF) - Intersil
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EL2020 Datasheet PDF : 14 Pages
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EL2020
differential gain/phase of 0.1% and 0.1°, but these are too
small to measure on single devices.
DIFFERENTIAL PHASE
OF 5 CASCADED
GAIN-OF-TWO STAGES
DIFFERENTIAL PHASE
OF 5 CASCADED
GAIN-OF-TWO STAGES
Video Distribution Amplifier
The distribution amplifier shown below features a difference
input to reject common mode signals on the 75Ω coax cable
input. Common mode rejection is often necessary to help to
eliminate 60Hz noise found in production environments.
To draw current out of pin 8 an “open collector output” logic
gate or a discrete NPN transistor can be used. This logic
interface method has the advantage of level shifting the logic
signal from 5V supplies to whatever supply the EL2020 is
operating on without any additional components.
Using the EL2020 as a Multiplexer
An interesting use of the enable feature is to combine
several amplifiers in parallel with their outputs common. This
combination then acts similar to a MUX in front of an
amplifier. A typical circuit is shown.
When the EL2020 is disabled, the DC output impedance is
very high, over 10kΩ. However there is also an output
capacitance that is non-linear. For signals of less than 5V
peak to peak, the output capacitance looks like a simple
15pF capacitor. However, for larger signals the output
capacitance becomes much larger and non-linear.
The example multiplexer will switch between amplifiers in
5µs for signals of less than ±2V on the outputs. For full
output signals of 20V peak to peak, the selection time
becomes 25µs. The disabled outputs also present a
capacitive load and therefore only three amplifiers can have
their outputs shorted together. However an unlimited number
can sum together if a small resistor (25Ω) is inserted in
series with each output to isolate it from the “bus”. There will
be a small gain loss due to the resistors of course.
VIDEO DISTRIBUTION AMPLIFIER WITH DIFFERENCE INPUT
EL2020 Disable/Enable Operation
The EL2020 has an enable/disable control input at pin 8. The
device is enabled and operates normally when pin 8 is left
open or returned to pin 7, VCC. When more than 250µA is
pulled from pin 8, the EL2020 is disabled. The output
becomes a high impedance, the inverting input is no longer
driven to the positive input voltage, and the supply current is
halved. To make it easy to use this feature, there is an
internal resistor to limit the current to a safe level (~1.1mA) if
pin 8 is grounded.
USING THE EL2020 AS A MULTIPLEXER
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