Again on December 3, 2024, a Design Concept (DI) was printed, “Single-supply single-ended inputs to pseudo class A/B differential output amp,” which created some dialogue about utilizing the circuit as a full wave rectifier.
DI editor Aalyia has kindly allowed a follow-up dialogue a couple of circuit which may very well be utilized for this, however is best suited to square-law capabilities.
The circuit proven in Determine 1 is an LTspice implementation constructed round a bipolar differential amplifier with Q1 and Q3 serving because the + and – lively differential enter units, respectively.
Determine 1 An LTspice implementation constructed round a bipolar differential amplifier with Q1 and Q3 serving because the + and – lively differential enter units, respectively, permitting the circuit to be higher suited to square-law capabilities.
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Extra units Q2 and This fall are added on the “middle level” between Q1 and Q3, and act such that the collector currents of all units are equal when no differential voltage is current.
This happens as a result of resistors R7 and R8 create a digital differential zero-volt “middle level” between the + and – differential inputs, and all system Vbe’s are the identical, neglecting the small voltage drop throughout R7 and R8 because of Q2 and This fall base bias currents.
R7 and R8 set the differential enter impedance for the circuit configuration, the place R1 and R3 set the sign supply differential impedances for the simulations.
The system emitter currents are managed by the “tail present supply” I1 at 4 mA; thus, every system has an emitter present of ~1 mA with zero differential enter. Be aware the -Diff Enter sign is created by utilizing a voltage-controlled voltage supply with an efficient acquire of -1 because of the inverted sensing of the +Diff Enter voltage (VIN+). This association permits the enter sign to be absolutely differential when LTspice controls the VI+ voltage supply throughout sign sweeps.
This isn’t a part of the circuit however used for comparisons: Voltage-controlled present supply, B1, is configured to provide a perfect square-law attribute by squaring the differential voltage (Vin+ –Vin-) and scaling by issue “Ok”.
Determine 2 exhibits the simulation outcomes of sweeping the differential enter voltage sources from -200 mV to +200 mV whereas monitoring the varied system currents. Be aware the differential output present, which is:
[Ic(Q1)+Ic(Q3)] – [Ic(Q2)+Ic(Q4)]
carefully approximates the perfect square-law with a scale issue of 0.3 (amps/volt) for differential enter voltages of ±60 mV.
Determine 2 Simulation outcomes of sweeping the differential enter voltage sources from -200 mV to +200 mV whereas monitoring the varied system currents.
Please observe this circuit is a transconductor kind the place the output is a differential present managed by a differential enter voltage.
Anyway, because of Aalyia for permitting us to observe up with this DI, and hopefully some of us will discover this and the earlier circuits fascinating.
Michael A Wyatt is a life member with IEEE and has continued to take pleasure in electronics ever since his childhood. Mike has a protracted profession spanning Honeywell, Northrop Grumman, Insyte/ITT/Exelis/Harris, ViaSat and retiring (semi) with Wyatt Labs. Throughout his profession he collected 32 US Patents and up to now printed just a few EDN Articles together with Finest Concept of the Yr in 1989.
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