OPA628 Burr-Brown, OPA628 Datasheet - Page 9

• Manufacturer Part Number: OPA628
• Description: Low Distortion Wideband OPERATIONAL AMPLIFIER
• Manufacturer: Burr-Brown

FIGURE 1. Configuration For Testing Differential Gain/Phase.
shown in Typical Performance Curves. Include the contribu-
tion of the feedback resistance when calculating the effec-
tive load resistance at the amplifier output. A high perfor-
mance spectrum analyzer such as the HP3585B should be
used to measure distortion.
Two-tone, third-order intermodulation distortion (IM) is an
important parameter for many RF amplifier applications.
The specification table shows the OPA628’s two-tone, third
order IM intercept at 5MHz and 10MHz. For these measure-
ments, tones were spaced 200kHz apart. This data is particu-
larly useful for determining the magnitude of the third-order
IM products. The magnitude of the third-order IM products
can be easily calculated from the expression:
As an example, with OPI
third order IM = 2(60 – 10) = 100dB below either 10dBm
tone. The OPA628’s low IM makes the device an excellent
choice for a variety of RF signal processing applications. In
order to obtain the full low distortion performance of the
OPA628, it is imperative to follow the recommendations
described in the “Printed Circuit Board Guidelines” section.
OUTPUT DRIVE CAPABILITY
The OPA628 has been optimized for low distortion perfor-
mance with back terminated 50
100
driving 6Vpp into a 50
This high-output drive capability makes the OPA628 an
ideal choice for a wide range of RF, IF, and video applica-
tions. All transmission lines should be terminated with the
characteristic impedance of the transmission line.
Internal current-limiting circuitry limits output current to
about 130mA at 25 C. This prevents damage from acciden-
where OPI
and 150
Third IM = third-order intermodulation ratio
+
P
TSG 130A
O
Tektronix
75
3
below each output tone, dB
Third IM = 2(OPI
= output level/tone, dBm/tone
P = third-order output intercept, dBm
respectively). However, it is capable of
3
load with a sacrifice in distortion.
P = 60dBm, for P
75
and 75
3
P – P
510
0.1µF
O
)
O
loads (R
= 10dBm, the
1
2
3
4
LOAD
–5V
OPA628
510
C = 10µF
DUT
=
9
tal shorts to common and eliminates the need for external
current-limiting circuitry. Although the device can with-
stand momentary shorts to either power supply, it is not
recommended.
Many demanding high-speed applications such as ADC/
DAC buffers require op amps with low wideband output
impedance. For example, low output impedance is essential
when driving the signal-dependent capacitances at the inputs
of flash A/D converters. As shown in Figure 2, the OPA628
maintains very low closed-loop output impedance over fre-
quency. Closed-loop output impedance increases with fre-
quency since loop gain is decreasing with frequency.
NOISE FIGURE
The OPA628’s voltage and current noise spectral densities
are specified in the Typical Performance Curves. For RF
applications, however, Noise Figure (NF) is often the pre-
ferred noise specification since it allows system noise per-
formance to be more easily calculated. The OPA628’s Noise
Figure vs Source Resistance is shown in Figure 3 for
frequencies above 1MHz.
FIGURE 2. Small Signal Output Impedance vs Frequency.
0.1µF
8
7
6
5
0.1µF
100m
100µ
10m
10µ
C = 10µF
1m
10
1
V
100
O
0.1µF
+5V
1k
10k
75
Frequency (Hz)
100k
G = +5V/V
OPA628
1M
75
Tektronix
VM700A
10M
G = +2V/V
G = +1V/V
100M
®