Wilson current mirror

Addition of a cascode transistor to the simple current mirror increases the output impedance (immunity to output voltage variation) because the collector voltages of the lower pair are fixed. The cascode transistor doesn't need to be matched - but it helps.

hFEMinTypMax
NPNSSM2210P300605 
BC184L100  
PNPSSM2220P80165 
BC214L140 400

βmβcIout
Iprog
%
3001000.9871.3
6051000.9841.6
801401.0101.0
804001.0202.0
1651400.9980.2
1654001.0070.7
1001001.0000.0

βm = Current Gain (hFE) of matched pair

βc = Current Gain (hFE) of cascode transistor