OPA4650 Datasheet, PDF (11/14 Pages) Burr-Brown (TI) – Wideband, Low Power, Quad Voltage Feedback OPERATIONAL AMPLIFIER

DIFFERENTIAL GAIN AND PHASE
Differential Gain (DG) and Differential Phase (DP) are
among the more important specifications for video applica-
tions. The percentage change in closed-loop gain over a
specified change in output voltage level is defined as DG.
DP is defined as the change in degrees of the closed-loop
phase over the same output voltage change. For the OPA4650,
DG and DP are both specified at the NTSC color sub-carrier
frequency of 3.58MHz and measured using industry stan-
dard video test equipment.
DISTORTION
The OPA4650’s harmonic distortion characteristics for a
100Ω load are shown in the Typical Performance Curves.
Distortion can be improved by increasing the load resistance
as illustrated in Figure 5. Remember to include the contribu-
tion of the feedback network when calculating the effective
load resistance seen by the amplifier.
–50
(f_O = 5MHz, 2Vp-p)
–60
–70
2f_O
–80
3f_O
–90
10
100
1k
Load Resistance (Ω)
FIGURE 5. Harmonic Distortion vs Load Resistance.
CROSSTALK
Crosstalk is the undesired coupling of one channel’s signal
into the output of the other channels. Crosstalk is a consid-
eration in all multichannel integrated circuits. The effect of
crosstalk is measured by driving one (“channel-to-channel”)
or more (“all-hostile”) channels and observing the output of
the undriven channel. The magnitude of this effect is ex-
pressed in the crosstalk specification as decibels of gain.
“Input referred” points to the fact that there is a direct
correlation between gain and crosstalk, therefore output
crosstalk increases proportionally at higher gains.
In quad devices, the effect of all-hostile crosstalk is observed
by driving all three channels concurrently and measuring the
output of the undriven fourth channel. The plots in Figure 6
illustrate both channel-to-channel and all-hostile crosstalk
for the OPA4650.
–30
G = +1
–40
All Hostile
–50
–60
Channel-to-Channel
–70
–80
0.1
1
10
Frequency (Hz)
100 300
FIGURE 6. Channel-to-Channel Isolation and All Hostile
Crosstalk.
NOISE FIGURE
The voltage and current noise spectral density are shown in
the Typical Performance Curves. For RF and IF applica-
tions, however, Noise Figure (NF) is often the preferred
specification. This specification shows a degradation in
SNR through a device relative to the thermal noise of the
source impedance alone.
The NF for the OPA4650, using 1MHz spot noise numbers
and an unterminated non-inverting input, is shown in
Figure 7.
30
NF = 10 LOG 1 + ^{en2 + (InRS)2}
25
4KTR_S
20
15
10
5
0
10
100
1k
10k
Source Resistance (Ω)
100k
FIGURE 7. Noise Figure vs Source Resistance.
SPICE MODELS AND EVALUATION BOARD
Computer simulation using SPICE is often useful when
analyzing the performance of analog circuits and systems.
This is particularly true for Video and RF amplifier circuits
where parasitic capacitance and inductance can have a
major effect on circuit performance. SPICE models and
evaluation PC boards are available for the OPA4650. Con-
tact the Burr-Brown Applications Department to receive a
SPICE diskette.
DEMONSTRATION BOARD
DEM-OPA465xP
DEM-OPA465xU
PACKAGE
8-Pin DIP
SO-8
PRODUCT
OPA4650P
oPA4650U
®
11
OPA4650