HA17301P Datasheet, PDF (4/14 Pages) Hitachi Semiconductor – Quad Operational Amplifier

HA17301P
HA17301P Application Examples
The HA17301P is a quad operational amplifier, and consists of four operational amplifier circuits and one
bias current circuit. The HA17301P features a wide operating temperature range, single-voltage power
supply operation, internal phase compensation, a wide zero-cross bandwidth, a low input bias current, and a
high open-loop gain. Thus the HA17301P can be used in a wide range of applications. This section
describes several applications using the HA17301P.
HA17301 Circuit Operation
V_CC
C₁
3 pF
Inverting input
3
Q₁
Non inverting
input
2
Q₃
D₁
GND
Bias circuit
Q₅
Q₄
Q₂
4
Output
Q₁₀
Op amp 1
Figure 1 HA17301 Internal Equivalent Circuit
Figure 1 shows the internal equivalent circuit for the HA17301P bias circuit and one operational amplifier
circuit (Op amp 1).
Op amp 1 is basically an emitter ground type operational amplifier in which the input transistor Q₁, the
buffer transistor Q₄, the current source transistor Q₅, the output emitter-follower transistor Q₂, and the
current source transistor Q₁₀ form an inverting amplifier. The voltage gain of this circuit is all given by the
transistor Q₁, and the adoption of the current-supply load Q₅ allows this circuit to provide a large open-loop
gain even at low power-supply voltages. Next, the emitter-follower transistor Q₂ lowers the output
impedance of this circuit. The use of the power-supply transistor Q₁₀ as the load for Q₂ gives this circuit an
extremely large dynamic range, and essentially an amplitude from ground to (V_CC – 1) can be acquired.
Also, the buffer transistor Q₄ is used to reduce the input current without increasing the DC input voltage
level. Since the capacitor C₁ is used to preserve stability when this inverting amplifier is used as a closed
circuit, no external compensation is required.
Now consider the non inverting circuit. Assuming that the current amplification ratio provided by Q₃ is
adequately large for the current flowing into the non inverting input, then all that current will flow through
diode D₁ and the voltage drop induced in the diode D₁ by this input current will be applied to the Q₃ base-
emitter junction. Therefore, if D₁ and Q₃ are matched, a current equal to the input current will flow in the
Q₃ emitter. Assuming that the current amplification ratio provided by Q₃ is adequately large, a current equal
to the input current will flow in the Q₃ collector. This is called a “current mirror”, and when an external
feedback resistor is used, a current equal to the non inverting input current will flow in this resistor and thus
determine the output voltage.
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