SHC615 Datasheet, PDF (14/20 Pages) Burr-Brown (TI) – Wide-Bandwidth, DC RESTORATION CIRCUIT

+V_CC
(13)
+V_CC
(13)
Biasing
Biasing
B
+1
E
C
(3)
(2)
(12)
B
(3)
+V_CC
(5)
(a)
Biasing
–V_CC
(5)
FIGURE 1. a) Simplified Block; and, b) Circuit Diagram of the OTA Section.
E
C
(2)
(12)
Biasing
(b)
V+
R_B
V_I
R_B
R_L
V_O
Inverting Gain
V_OS ≈ several volts
R_E
V_I
100Ω _{3 B}
12
C
OTA
E
2
R_E
V_O
Non-InvertingGain
R_L
V_OS ≈ 0
V–
(a) Common Emitter Amplifier
Transconductance varies over temperature.
(b) Common-E Amplifier
Transconductance remains constant over temperature.
FIGURE 2. a) Common Emitter Amplifier Using a Discrete Transistor; b) Common-E Amplifier Using the OTA Portion of the
SHC615.
BASIC APPLICATIONS CIRCUITS
Most application circuits for the OTA section consist of a
few basic types which are best understood by analogy to
discrete transistor circuits. Just as the transistor has three
basic operating modes—common emitter, common base,
and common collector—the OTA has three equivalent oper-
ating modes common-E, common-B, and common-C (See
Figures 2, 3 and 4). Figure 2 shows the OTA connected as
a Common-E amplifier which is equivalent to a common
emitter transistor amplifier. Input and output can be ground
referenced without any biasing. Due to the sense of the
output current, the amplifier is non-inverting.
Figure 4 shows the common-B amplifier. This configuration
produces an inverting gain, and the input is low-impedance.
When a high impedance input is needed, it can be created by
inserting a buffer amplifier like BUF600 in series.
®
SHC615
14