Datasheet
AD8336
Rev. C | Page 23 of 28
Circuit Configuration for Inverting Gain
The preamplifier can also be used in an inverting configuration,
as shown in Figure 81.
PRAO
34dB
AD8336
PREAMPLIFIER
INPP
4
5
+
–
8
VOUT
1
9
GAIN = 9.6dB INPN
R
FB1
100Ω
R
FB2
301Ω
–60dB TO 0dB
13
VPOSVNEG
10
+5V
–5V
PWRAVGAI
2 3
VCOM
06228-081
Figure 81. Circuit Configuration for Inverting Gain
The considerations regarding total resistance vs. distortion, noise,
and power that were noted in the noninverting case also apply
in the inverting case, except that the amplifier can be operated
at unity inverting gain. The signal gain is reduced while the
noise gain is the same as for the noninverting configuration:
FB1
FB2
R
R
GainSignal =
and
1+=
FB1
FB2
R
R
GainNoise
USING THE POWER ADJUST FEATURE
The AD8336 has the provision to operate at lower power with a
trade-off in bandwidth. The power reduction applies to the preamp
and the VGA sections, and the bandwidth is reduced equally
between them. Reducing the power is particularly useful when
operating with higher supply voltages and lower values of output
loading that would otherwise stress the output amplifiers. When
Pin PWRA is grounded, the amplifiers operate in their default
mode, and the combined 3 dB bandwidth is 80 MHz with the
preamp gain adjusted to 4×. When the voltage on Pin PWRA is
between 1.2 V and 5 V, the power is reduced by approximately
half and the 3 dB bandwidth reduces to approximately 35 MHz.
The voltage at Pin PWRA must not exceed 5 V.
DRIVING CAPACITIVE LOADS
The output stages of the AD8336 are stable with capacitive loads
up to 47 pF for a supply voltage of ±3 V and with capacitive loads
up to 10 pF for supply voltages up to ±8 V. For larger combined
values of load capacitance and/or supply voltage, a 20 series
resistor is recommended for stability.
The influence of capacitance and supply voltage are shown in
Figure 50 and Figure 51, where representative combinations of
load capacitance and supply voltage requiring a 20 resistor
are marked with an asterisk. No resistor is required for the ±3 V
plots in Figure 49, but a resistor is required for most of the ±12 V
plots in Figure 51.