Datasheet

R
1
160
Ω
V
I
V
O
3 B
2
E
C
8
R
E
78
Ω
R
C
500
Ω
G = 5V/V
I
Q
= 11.2mA
OTA
100
Ω
V
I
V+
V
−
V
I
V
O
3 B
2
E
C
8
R
S
R
S
R
L
R
E
V
O
R
E
R
L
Inverting Gain
V
OS
= Several Volts
Noninverting Gain
V
OS
= 0V
(a) Common−Emitter Amplifier
Transconductance varies over temperature.
(b) Common−E Amplifier
Transconductance remains constant over temperature.
OTA
g
m_deg
+
1
1
g
m
) R
E
(2)
G=
AtI =11.2mA
Q
G=atI =11.2mA
Q
V
I
V
O
3
2
8
R
E
r
E
R
L2
R
1
100W
R
IN
50W
R =R +R ||R
L L1 L2 IN
OTA
R
L1
Network
Analyzer
R
L
R +r
E E
R
L
R +8W
E
r ==8W
E
1
102mA/V
1
g
m
r =
E
OPA860
SBOS331C – JUNE 2005 – REVISED AUGUST 2008 ....................................................................................................................................................... www.ti.com
The forward amplifier shown in Figure 48 and
Figure 49 corresponds to one of the basic circuits
used to characterize the OPA860. Extended
characterization of this topology appears in the
Typical Characteristics section of this data sheet.
Figure 48. Forward Amplifier Configuration and
Test Circuit
Figure 47. Common-Emitter vs Common-E
Amplifier
The transconductance of the OTA with degeneration
can be calculated by Equation 2 :
A positive voltage at the B-input, pin 3, causes a
positive current to flow out of the C-input, pin 8.
Figure 47 b shows an amplifier connection of the
OTA, the equivalent of a common-emitter transistor
amplifier. Input and output can be ground-referenced
Figure 49. Forward Amplifier Design Equations
without any biasing. The amplifier is noninverting
because of the sense of the output current.
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