OPA622AP BURR-BROWN [Burr-Brown Corporation], OPA622AP Datasheet - Page 13

• Manufacturer Part Number: OPA622AP
• Description: Wide-Bandwidth OPERATIONAL AMPLIFIER
• Manufacturer: BURR-BROWN [Burr-Brown Corporation]

without the feedback buffer produces the wider bandwidth
of the current-feedback concept. The additional signal delay
time through the feedback buffer determines the difference
in AC performance between voltage and current feedback.
The specifications for offset voltage, CMMR, and settling
times are the compromise for higher speed.
The open-loop gain for the current-feedback amplifier varies
directly with the closed-loop gain and can be adjusted by
changing the size of R
the open-loop gain can be adjusted to achieve bandwidth
independent of gain, but the effects of this adjustment
become limited when second-order effects start to dominate.
Figure 6 gives an overview of the OPA622 inverting and
non-inverting amplifier configurations and shows the equa-
tions for the closed-loop gains.
OPTIMAL FREQUENCY RESPONSE ADJUSTMENT
Conventional voltage-feedback op amps use a compensation
capacitor for stable unity-gain operation. During transitions,
the quiescent current charges and discharges this capacitor,
and both parameters determine the slew rate according to:
This method is not appropriate for wide-band op amps. The
slew rate and thus the large-signal behavior are significantly
reduced, and the bandwidth decreases with increasing closed-
loop gains according to the gain-bandwidth product.
FIGURE 6. Op Amp Configurations for OPA622.
SR =
2
||R
V
OUT
1
t
. For gains of less than 10V/V,
OTA
OTA
+V
+V
IN
IN
=
G
C
CL
I
FB
G
R
= 1 +
Non-inverting
Non-inverting
CL
OG
= 1 +
OB
OB
R
R
FB
2
1
R
R
2
1
V
R
R
V
R
R
OUT
OUT
2
1
2
1
Voltage-Feedback
Current-Feedback
13
OTA
OTA
Amplifiers with an external compensation capacitor allow
optimal frequency adjustment versus closed-loop gain, but
nevertheless do not significantly improve large-signal be-
havior. The most effective solution is to make the open-loop
gain (G
The widely-used current-feedback op amp type designed
with real complementary circuit techniques overcomes the
internal compensation capacitor and allows the feedback
network to set the open-loop gain. The ratio of the feedback
resistors determines the low-frequency closed-loop gain,
and the parallel impedance defines the amplifier’s open-loop
gain for stable operation and flat frequency response. A
nearly constant bandwidth can be achieved over a wide
range of closed-loop gains. However, current-feedback op
amps suffer from nonidentical inputs and poor input offset
and CMRR. The voltage-feedback op amp OPA622 with its
complementary topology features two identical high-imped-
ance inputs, lower input offset values, and improved CMRR.
The ratio of the feedback resistors determines the low-
frequency closed-loop gain, and the external resistor R
sets the open-loop gain to achieve a flat frequency response
over a wide range of closed-loop gains. Since R
selected, optimized pulse responses are possible even with
larger load capacitances. The OPA622 combines the slew
rate enhancements of a complementary amplifier design
with the precision of a voltage-feedback system.
The hybrid model shown in Figure 9 describes the AC
behavior of a noncompensated wide-band differential op
amp. The open-loop frequency response, which is illustrated
in Figure 10 for various R
G
CL
FB
OL
G
R
= –
OG
CL
) externally adjustable.
Inverting
Inverting
= –
R
R
2
1
OB
OB
FB
R
R
2
1
–V
–V
R
R
R
R
V
V
2
1
IN
2
1
IN
OUT
OUT
OG
values, is determined by two
OPA622
OG
can be
OG
®