Datasheet

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SBOS317D − SEPTEMBER 2004 − REVISED AUGUST 2008
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14
WIDEBAND SINGLE-SUPPLY OPERATION
Figure 3 shows the AC-coupled, single +5V supply, gain of
+2V/V circuit configuration used as a basis for the +5V only
Electrical and Typical Characteristics. The key require-
ment for single-supply operation is to maintain input and
output signal swings within the useable voltage ranges at
both the input and the output. The circuit of Figure 3
establishes an input midpoint bias using a simple resistive
divider from the +5V supply (two 806Ω resistors) to the
noninverting input. The input signal is then AC-coupled
into this midpoint voltage bias. The input voltage can swing
to within 0.9V of the negative supply and 0.6V of the
positive supply, giving a 3.5V
PP
input signal range. The
input impedance matching resistor (57.6Ω) used in
Figure 3 is adjusted to give a 50Ω input match when the
parallel combination of the biasing divider network is
included. The gain resistor (R
G
) is AC-coupled, giving the
circuit a DC gain of +1. This puts the input DC bias voltage
(2.5V) on the output as well. On a single +5V supply, the
output voltage can swing to within 1.3V of either supply pin
while delivering more than 60mA output current giving
2.4V output swing into 100Ω (5.6dBm maximum at a
matched 50Ω load).
Figure 4 shows the AC-coupled, single +5V supply, gain of
−1V/V circuit configuration used as a basis for the +5V only
Typical Characteristic curves. In this case, the midpoint
DC bias on the noninverting input is also decoupled with
an additional 0.01µF decoupling capacitor. This reduces
the source impedance at higher frequencies for the
noninverting input bias current noise. This 2.5V bias on the
noninverting input pin appears on the inverting input pin
and, since R
G
is DC blocked by the input capacitor, will
also appear at the output pin.
The single-supply test circuits of Figure 3 and Figure 4
show +5V operation. These same circuits can be used
over a single-supply range of +4V to +12.6V. Operating on
a single +12V supply, with the Absolute Maximum Supply
voltage specification of +13V, gives adequate design
margin for the typical ±5% supply tolerance.
+5V
+V
S
DIS
100
Ω
R
G
402
Ω
806
Ω
806
Ω
57.6
Ω
0.01
µ
F
+
6.8
µ
F0.1
µ
F
0.01
µ
F
V
I
50
Ω
Source
R
F
402
Ω
V
O
V
S
/2
1/4
OPA4820
Figure 3. AC-Coupled, G = +2V/V, Single-Supply Specifications and Test Circuit
+5V
+V
S
DIS
100
Ω
R
G
402
Ω
806
Ω
806
Ω
0.01
µ
F
0.01
µ
F
V
I
R
F
402
Ω
V
O
V
S
/2
+
6.8
µ
F0.1
µ
F
1/4
OPA4820
Figure 4. AC-Coupled, G = −1V/V, Single-Supply Specifications and Test Circuit