Op Amp Applications from Analog Devices - Get a Free Blog

SIGNAL AMPLIFIERS
VIDEO AMPLIFIERS
There are multiple criteria that must be met in designing the feedback network around the
AD8037. These are a specified gain, and a fixed offset which will enable the output swing
of the clamped amplifier to match the target input range of the converter.
The feedback resistor, R2 = 301Ω, is selected for optimum bandwidth per the data sheet
recommendation. For a gain of two, the parallel combination of R1 and R3 must also
equal R2:
(nearest 1% standard resistor value).
R1⋅R3 = R2
= 301Ω
, Eq. 6-29
R1+ R3
In addition, the Thevenin equivalent output voltage from the AD780 +2.5V reference and
the R3/R1 divider must be +1V, to provide the required –1V offset at the output of the
AD8037. This will cause the output swing of the AD8037 to be biased at –1V when VIN
is zero, and to range from 0 to –2V as VIN ranges from –0.5 to 0.5V.
25 . ⋅ R1
= 1volt
. Eq. 6-30
R1+ R3
Solving these equations yields resistance values of R1 = 499Ω, R3 = 750Ω, using the
nearest 1% standard values.
Other input and output voltages ranges can also be accommodated, by appropriate
changes in the external resistors.
Further fast clamping op amp application examples are given in Reference 9, and the
"Amplifier Ideas" section of this chapter (plus of course the device data sheets).
6.123