what your tolerance on matching parameters? 10% or 1% or something completely different?
What do you need to match? hFE or Vbe or both hFE and Vbe @ one specific current over over a range of currents?
If you're only matching Vbe to +-10mV then a batch of 20 will probably give you 6pairs. If you change your tolerance to +-1mV at two currents the yield is likely to drop, you might get 1pair or 6pairs, it's down to luck.
If you want to match hFE to 10% at one current, again a batch of 20 is likely to yield 6 pairs.
The tighter the tolerance and the more parameters that must be matched the lower the yield.
What do you need to match? hFE or Vbe or both hFE and Vbe @ one specific current over over a range of currents?
If you're only matching Vbe to +-10mV then a batch of 20 will probably give you 6pairs. If you change your tolerance to +-1mV at two currents the yield is likely to drop, you might get 1pair or 6pairs, it's down to luck.
If you want to match hFE to 10% at one current, again a batch of 20 is likely to yield 6 pairs.
The tighter the tolerance and the more parameters that must be matched the lower the yield.
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