CA3140AMZ データシートの表示（PDF） - Intersil
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CA3140AMZ Datasheet PDF : 22 Pages
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CA3140, CA3140A
Application Information
Circuit Description
As shown in the block diagram, the input terminals may be
operated down to 0.5V below the negative supply rail. Two
class A amplifier stages provide the voltage gain, and a
unique class AB amplifier stage provides the current gain
necessary to drive low-impedance loads.
A biasing circuit provides control of cascoded constant current
flow circuits in the first and second stages. The CA3140
includes an on chip phase compensating capacitor that is
sufficient for the unity gain voltage follower configuration.
Input Stage
The schematic diagram consists of a differential input stage
using PMOS field-effect transistors (Q9, Q10) working into a
mirror pair of bipolar transistors (Q11, Q12) functioning as load
resistors together with resistors R2 through R5. The mirror pair
transistors also function as a differential-to-single-ended
converter to provide base current drive to the second stage
bipolar transistor (Q13). Offset nulling, when desired, can be
effected with a 10kΩ potentiometer connected across
Terminals 1 and 5 and with its slider arm connected to Terminal
4. Cascode-connected bipolar transistors Q2, Q5 are the
constant current source for the input stage. The base biasing
circuit for the constant current source is described
subsequently. The small diodes D3, D4, D5 provide gate oxide
protection against high voltage transients, e.g., static electricity.
Second Stage
Most of the voltage gain in the CA3140 is provided by the
second amplifier stage, consisting of bipolar transistor Q13
and its cascode connected load resistance provided by
bipolar transistors Q3, Q4. On-chip phase compensation,
sufficient for a majority of the applications is provided by C1.
Additional Miller-Effect compensation (roll off) can be
accomplished, when desired, by simply connecting a small
capacitor between Terminals 1 and 8. Terminal 8 is also
used to strobe the output stage into quiescence. When
terminal 8 is tied to the negative supply rail (Terminal 4) by
mechanical or electrical means, the output Terminal 6
swings low, i.e., approximately to Terminal 4 potential.
Output Stage
The CA3140 Series circuits employ a broad band output stage
that can sink loads to the negative supply to complement the
capability of the PMOS input stage when operating near the
negative rail. Quiescent current in the emitter-follower cascade
circuit (Q17, Q18) is established by transistors (Q14, Q15)
whose base currents are “mirrored” to current flowing through
diode D2 in the bias circuit section. When the CA3140 is
operating such that output Terminal 6 is sourcing current,
transistor Q18 functions as an emitter-follower to source current
from the V+ bus (Terminal 7), via D7, R9, and R11. Under these
conditions, the collector potential of Q13 is sufficiently high to
permit the necessary flow of base current to emitter follower
Q17 which, in turn, drives Q18.
When the CA3140 is operating such that output Terminal 6 is
sinking current to the V- bus, transistor Q16 is the current
sinking element. Transistor Q16 is mirror connected to D6, R7,
with current fed by way of Q21, R12, and Q20. Transistor Q20,
in turn, is biased by current flow through R13, zener D8, and
R14. The dynamic current sink is controlled by voltage level
sensing. For purposes of explanation, it is assumed that output
Terminal 6 is quiescently established at the potential midpoint
between the V+ and V- supply rails. When output current
sinking mode operation is required, the collector potential of
transistor Q13 is driven below its quiescent level, thereby
causing Q17, Q18 to decrease the output voltage at Terminal 6.
Thus, the gate terminal of PMOS transistor Q21 is displaced
toward the V- bus, thereby reducing the channel resistance of
Q21. As a consequence, there is an incremental increase in
current flow through Q20, R12, Q21, D6, R7, and the base of
Q16. As a result, Q16 sinks current from Terminal 6 in direct
response to the incremental change in output voltage caused
by Q18. This sink current flows regardless of load; any excess
current is internally supplied by the emitter-follower Q18. Short
circuit protection of the output circuit is provided by Q19, which
is driven into conduction by the high voltage drop developed
across R11 under output short circuit conditions. Under these
conditions, the collector of Q19 diverts current from Q4 so as to
reduce the base current drive from Q17, thereby limiting current
flow in Q18 to the short circuited load terminal.
Bias Circuit
Quiescent current in all stages (except the dynamic current
sink) of the CA3140 is dependent upon bias current flow in R1.
The function of the bias circuit is to establish and maintain
constant current flow through D1, Q6, Q8 and D2. D1 is a diode
connected transistor mirror connected in parallel with the base
emitter junctions of Q1, Q2, and Q3. D1 may be considered as a
current sampling diode that senses the emitter current of Q6
and automatically adjusts the base current of Q6 (via Q1) to
maintain a constant current through Q6, Q8, D2. The base
currents in Q2, Q3 are also determined by constant current flow
D1. Furthermore, current in diode connected transistor Q2
establishes the currents in transistors Q14 and Q15.
Typical Applications
Wide dynamic range of input and output characteristics with
the most desirable high input impedance characteristics is
achieved in the CA3140 by the use of an unique design based
upon the PMOS Bipolar process. Input common mode voltage
range and output swing capabilities are complementary,
allowing operation with the single supply down to 4V.
The wide dynamic range of these parameters also means
that this device is suitable for many single supply
applications, such as, for example, where one input is driven
below the potential of Terminal 4 and the phase sense of the
output signal must be maintained – a most important
consideration in comparator applications.
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