OPA2695 Datasheet, PDF (20/40 Pages) Texas Instruments – Dual, Ultra-Wideband, Current-Feedback OPERATIONAL AMPLIFIER with Disable

OPA2695
SBOS354 – APRIL 2008..................................................................................................................................................................................................... www.ti.com
+5V
+V_S
0.1mF
6.8mF
20W
DIS
50W Load
1/2
V_O ^50W
OPA2695
50W Source
V_I
R_G
54.9W
R_T
562W
Optional
0.01mF
R_F
442W
0.1mF
6.8mF
-V_S
-5V
Figure 69. DC-Coupled, G = –8V/V, Bipolar Supply
Specifications and Test Circuit
Figure 70 shows the ac-coupled, single +5V supply,
gain of +8V/V circuit configuration used as a basis for
the +5V only Electrical Characteristics and Typical
Characteristics. The key requirement for broadband
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 70 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 1.6V of
either supply pin, giving a 1.8V_PP input signal range
centered between the supply pins. The input
impedance matching resistor (57.6Ω) used in
Figure 70 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 configuration
puts the input dc bias voltage (2.5V) on the output as
well. The feedback resistor value has been adjusted
from the bipolar supply condition to re-optimize for a
flat frequency response in +5V only, gain of +8
operation (see Setting Resistor Values to Optimize
Bandwidth). On a single +5V supply, the output
voltage can swing to within 1.0V of either supply pin
while delivering more than 90mA output current,
giving 3V output swing into 100Ω (7dBm maximum at
the matched load). The circuit of Figure 70 shows a
blocking capacitor driving into a 50Ω output resistor,
then into a 50Ω load. Alternatively, the blocking
capacitor could be removed with the load tied to a
supply midpoint or to ground if the dc current required
by this grounded load is acceptable.
+5V
+V_S
50W Source
V_I
0.1mF
57.6W ^1000pF
806W
806W
0.1mF
6.8mF
DIS
1/2
OPA2695
V_O ^0.1mF
R_F
348W
1000pF
50W Load
50W
R_G
50W
1000pF
0.1mF
Figure 70. AC-Coupled, G = +8V/V, Single-Supply Specifications and Test Circuit
20
Submit Documentation Feedback
Product Folder Link(s): OPA2695
Copyright © 2008, Texas Instruments Incorporated