AD8610/AD8620
Rev. F | Page 13 of 24
THEORY OF OPERATION
+
–
V
IN
0V p-
3
2
U1
+13V
–13V
R4
2kΩ
R2
2kΩ
R1
20kΩ
R3
2kΩ
U2
5
6
7
V+
V–
V–
V+
CS (dB) = 20 log (V
OUT
/ 10 × V
IN
)
2730-041
Figure 41. Channel Separation Test Circuit
FUNCTIONAL DESCRIPTION
The AD8610/AD8620 are manufactured on the Analog Devices,
Inc., XFCB (eXtra fast complementary bipolar) process. XFCB
is fully dielectrically isolated (DI) and used in conjunction with
N-channel JFET technology and thin film resistors (that can be
trimmed) to create the JFET input amplifier. Dielectrically isolated
NPN and PNP transistors fabricated on XFCB have an f
τ
> 3 GHz.
Low TC thin film resistors enable very accurate offset voltage and
offset voltage temperature coefficient trimming. These process
breakthroughs allow Analog Devices IC designers to create an
amplifier with faster slew rate and more than 50% higher band-
width at half of the current consumed by its closest competition.
The AD8610/AD8620 are unconditionally stable in all gains,
even with capacitive loads well in excess of 1 nF. The AD8610B
grade achieves less than 100 V of offset and 1 V/°C of offset
drift, numbers usually associated with very high precision bipolar
input amplifiers. The AD8610 is offered in the tiny 8-lead MSOP
as well as narrow 8-lead SOIC surface-mount packages and is
fully specified with supply voltages from ±5.0 V to ±13 V. The
very wide specified temperature range, up to 125°C, guarantees
superior operation in systems with little or no active cooling.
The unique input architecture of the AD8610/AD8620 features
extremely low input bias currents and very low input offset voltage.
Low power consumption minimizes the die temperature and
maintains the very low input bias current. Unlike many competi-
tive JFET amplifiers, the AD8610/AD8620 input bias currents are
low even at elevated temperatures. Typical bias currents are less
than 200 pA at 85°C. The gate current of a JFET doubles every
10°C, resulting in a similar increase in input bias current over
temperature. Give special care to the PC board layout to minimize
leakage currents between PCB traces. Improper layout and
board handling generates a leakage current that exceeds the bias
current of the AD8610/AD8620.
138
136
120
128
126
124
122
132
130
134
02730-042
CS (dB)
FREQUENCY (kHz)
0 100 150 20050 250 300 350
Figure 42. AD8620 Channel Separation Graph
Power Consumption
A major advantage of the AD8610/AD8620 in new designs is
the power saving capability. Lower power consumption of the
AD8610/AD8620 makes them much more attractive for portable
instrumentation and for high density systems, simplifying thermal
management, and reducing power-supply performance require-
ments. Compare the power consumption of the AD8610 vs. the
OPA627 in Figure 43.
8
7
2
6
5
4
3
02730-043
SUPPLY CURRENT (mA)
TEMPERATURE (°C)
–75 –25 0 25–50 50 75 100 125
OPA627
AD8610
Figure 43. Supply Current vs. Temperature
