CA3060 View Datasheet(PDF) - Intersil
Part Name
Description
Manufacturer
CA3060 Datasheet PDF : 12 Pages
| |||
CA3060
Application Information
The CA3060 consists of three operational amplifiers similar
in form and application to conventional operational amplifiers
but sufficiently different from the standard operational
amplifier (op amp) to justify some explanation of their
characteristics. The amplifiers incorporated in the CA3060
are best described by the term Operational Transconduc-
tance Amplifier (OTA). The characteristics of an ideal OTA
are similar to those of an ideal op amp except that the OTA
has an extremely high output impedance. Because of this
inherent characteristics the output signal is best defined in
terms of current which is proportional to the difference
between the voltages of the two input terminals. Thus, the
transfer characteristics is best described in terms of
transconductance rather than voltage gain. Other than the
difference given above, the characteristics tabulated are
similar to those of any typical op amp.
The OTA circuitry incorporated in the CA3060 (Figure 18)
provides the equipment designer with a wider variety of
circuit arrangements than does the standard op amp;
because as the curves indicate, the user may select the
optimum circuit conditions for a specific application simply by
varying the bias conditions of each amplifier. If low power
consumption, low bias, and low offset current, or high input
impedance are primary design requirements, then low
current operating conditions may be selected. On the other
hand, if operation into a moderate load impedance is the
primary consideration, then higher levels of bias may be
used.
Q11
D5
Q7
Q10
Q3
INVERTING
D2
INPUT
-
Q2
D3
Q5 Q9
AMPLIFIER
BIAS
CURRENT
(ABC)
+
Q4
NON-
Q1
INVERTING
INPUT
D1
Q6
Q8
D6
D7
Q14
D8
V+
Q15
Q13
OUTPUT
Q12
D4
V-
COMPLETE OTA CIRCUIT
V-
FIGURE 18. COMPLETE SCHEMATIC DIAGRAM SHOWING BIAS
REGULATOR AND ONE OF THE THREE
OPERATIONAL TRANSCONDUCTANCE AMPLIFIERS
Bias Consideration for Op Amp Applications
The operational transconductance amplifiers allow the circuit
designer to select and control the operating conditions of the
circuit merely by the adjustment of the amplifier bias current
IABC. This enables the designer to have complete control
over transconductance, peak output current and total power
consumption independent of supply voltage.
In addition, the high output impedance makes these amplifi-
ers ideal for applications where current summing is involved.
The design of a typical operational amplifier circuit (Figure
19) would proceed as follows:
Circuit Requirements
Closed Loop Voltage Gain = 10 (20dB)
Offset Voltage Adjustable to Zero
Current Drain as Low as Possible
Supply Voltage = ±6V
Maximum Input Voltage = ±50mV
Input Resistance = 20kΩ
Load Resistance = 20kΩ
Device: CA3060
+6V
0.1
INPUT
RS
20kΩ
13 -
3
RF
200kΩ
+6V
ROFFSET
<4MΩ
2.2MΩ
-6V
14
18kΩ
0.1
AMPLIFIER
16
1
+
15
8
RABC
560kΩ
-6V
RL
20kΩ
TO +6V
FIGURE 19. 20dB AMPLIFIER USING THE CA3060
Calculation
1. Required Transconductance g21. Assume that the
open loop gain AOL must be at least ten times the closed
loop gain. Therefore, the forward transconductance
required is given by:
g21 = AOL/RL
= 100/18kΩ
≅ 5.5mS
(RL = 20kΩ in parallel with 200kΩ ≅ 18kΩ)
2. Selection of Suitable Amplifier Bias Current. The ampli-
fier bias current is selected from the minimum value curve
of transconductance (Figure 11) to assure that the amplifi-
er will provide sufficient gain. For the required g21 of
5.5mS an amplifier bias current IABC of 20µA is suitable.
3. Determination of Output Swing Capability. For a
closed loop gain of 10 the output swing is ±0.5V and the
peak load current is 25µA. However, the amplifier must
also supply the necessary current through the feedback
resistor and if RS = 20kΩ, then RF = 200kΩ for ACL = 10.
Therefore, the feedback loading = 0.5V/200kΩ = 2.5µA.
The total amplifier current output requirements are, there-
fore, ±27.5µA. Referring to the data given in Figure 5, we
see that for an amplifier bias current of 20µA the amplifier
output current is ±40µA. This is obviously adequate and it
is not necessary to change the amplifier bias current
IABC.
3-7
Share Link: 