Amplification factor for common emitter amplifier

On Tue, 20 Aug 2019 19:32:37 +0100, "Kevin Aylward"
<kevinRemovAT@kevinaylward.co.uk> wrote:

>"John Larkin"  wrote in message 
>news:somllehqm0ggs82tmrf1e20smdjt4lq0jk@4ax.com...
>
>>
>>Well, yeah; usually with other components around 'em.   LM13700 (and OTA 
>>clones
>>with several other part numbers) are basically current mirrors with 
>>differential-input
>>polarity switching.   Put half a volt delta-V on the inputs, and the output 
>>current
>>is slave to the current-program input pin.
>
>>That's cute, but the the Gm spec of the LM13700 covers about a 2:1
>>range. The bias mirror alone may be better.
>
>>Once you are willing to buy an opamp, you can make an arbitrarily
>>accurate current mirror.
>
>Sometimes used in CMOS design, where one has a not bad npn, but no decent 
>pnp but you need a low noise top side current source. The opamp can loop 
>around a pmos with the noise of the npn.
>
>-- Kevin Aylward
>http://www.anasoft.co.uk - SuperSpice
>http://www.kevinaylward.co.uk/ee/index.html
>

One fun circuit uses the V+ supply pin of the opamp as the current
output, so it has one amp and two resistors. There is a little Iq
error. That circuit can be cascoded too.

Two of those can make the perfect class B signal splitter.