OPA660 Burr-Brown, OPA660 Datasheet - Page 10

• Manufacturer Part Number: OPA660
• Description: Wide Bandwidth OPERATIONAL TRANSCONDUCTANCE AMPLIFIER AND BUFFER
• Manufacturer: Burr-Brown

using this more complex biasing circuitry. It does, however,
demonstrate the possibility of signal-controlled quiescent
current. This may suggest other possibilities such as AGC,
dynamic control of AC behavior, or VCO.
Figure 4 shows logic control of pin 1 used to disable the
OPA660. Zero/5V logic levels are converted to a 1mA/0mA
current connected to pin 1. The 1mA current flowing in R
increases the voltage at pin 1 to approximately 1V above the
–5V rail. This will reduce I
OPA660.
BASIC APPLICATIONS CIRCUITS
Most applications circuits for the OTA section consist of a
few basic types which are best understood by analogy to a
transistor. Just as the transistor has three basic operating
modes—common emitter, common base, and common col-
lector—the OTA has three equivalent operating modes com-
mon-E, common-B, and common-C. See Figures 5, 6, and 7.
FIGURE 5. Common-Emitter vs Common-E Amplifier.
FIGURE 6. Common-Collector vs Common-C Amplifier.
V
I
(a) Common-Collector Amplifier
(Emitter Follower)
R
E
V+
V–
®
V
Transconductance varies over temperature.
G
V
I
OPA660
OS
R
R
1
B
B
V
V
(a) Common-Emitter Amplifier
0.7V
I
O
100
V+
V–
Q
to near zero, disabling the
3
(b) Common-C Amplifier
B
(Buffer)
R
R
R
G =
R
Inverting Gain
V
E
L
E
O
OS
=
V
1 +
O
OTA
several volts
8
C
E
g
2
1
m
g
1
m
1
¥ R
G
V
E
OS
V
O
1
0
Q
V
I
10
100
FIGURE 4. Logic-Controlled Disable Circuit.
Transconductance remains constant over temperature.
FIGURE 7. Common-Base vs Common-B Amplifier.
V
5V: OPA660 On
I
3
Logic In
(a) Common-Base
0/5V
B
(b) Common-E Amplifier
Amplifier
V+
I = 0: OPA660 On
I
4.7k
C
C
R
E
R
R
Non-Inverting Gain
V
L
E
I
1mA: OPA660 Off
OS
C
OTA
C
8
E
2
+5V
2N2907
several volts
V
O
100
100
R
V
L
3
I
G = –
B
V
O
(b) Common-B Amplifier
Non-Inverting Gain
V
1
Current Source
OS
R
250
R
E
OTA
8
C
E
2
Circuitry
Q
Internal
+
R
R
0
50k
–5V
L
E
g
1
m
–
R
R
R
Inverting Gain
L
E
4
L
OPA660
V
OS
V
O
0