SparkoS Labs has created a range of discrete DIP8-mounted OPAs optimized to deliver excellent audio performance. They will allow you to replace less powerful OPA or quite simply to obtain a different sound. Moreover, with their reduced dimensions, measuring a third of the size of any other discrete OPA, they will integrate without problem in your devices and projects.
Class A biasing and high output current capacity, coupled with a proprietary compensation system requiring multiple NPO dielectric capacitors make these discrete amplifiers impossible to manufacture as monolithic integrated circuits.
SparkoS Labs Technology
All of SparkoS Labs OPAs are bases on Lin 3 Stage topology consisting of an input stage differential pair, a gain stage (VAS) and an output stage, all biased in Class A with two pole compensation. All active components are Bipolar Junction Transistors (BJT) to obtain the greatest linearity. Components are fully protected from over current by active current limit circuitry in the output and gain stages. They are also protected from large differential input voltages by high-speed Schottky diodes.
Input stage :
The input stage of the SparkoS Labs OPAs contain a dual matched pair of NPN BJTs. Input offset voltage is factory trimmed and typically turns out to be better than 250uV @+/- 12VCC. A cascode Wilson current mirror is utilized as the active load for the input differential pair, for precise current matching between the input pair transistors.
Gain stage (VAS) :
The gain stage is a cascode loaded Darlington for the highest linearity and open loop gain possible. The cascode biasing voltage is derived from precision shunt references, wihch have a much lower dynamic impedance and lower noise than the low voltage Zener diodes which are commonly used to derive the bias voltage. The gain stage is also current limited for a better stability.
Output stage :
The output stage is a push-pull emitter-follower biased in Class A with 8mA standing current. Due to push-pull action, the output stage can source or sink 16mA of current and still remain in class A mode. The output stage will automatically revert to class AB in th event that more output current is demanded. Active current limiting is employed in the output stage to protect it from an over current situation. The output transistors are high gain individual devices in SOT23 package, manufactured by Diodes, Inc. who have developed an encapsulation methode to dissipate two to three times the power of a typical SOT23 packaged components. By using these output components, SparkoS Labs OPAs can have a high Class A bias current and the ability to source or sink far more output current than comparable monolithic IC.
All the discret OPAs from SparkoS Labs empliy a uniquely implement 2 pole compensation scheme tjat is extremely tolerant of capacitive loading. This allows these discrete OPAs to be used on many PCB in many projects without any stability issue. Two pole compensation despite its superirority ton single pole schemes, in not often used in monolithic OPAs because of the fabrication difficulty. Capacitors in monolitics OPAs consume a large amount of space on the die so it isn't possible to add more capacitors. SparkoS Labs OPAs are using 3 compensation capacitors so it's not possible to fabricate these OPAs as monolothics IC.