PMOS source degenerated current mirror

From ICclopedia

Schematic Diagram[edit]

Circuit Netlist[edit]

* dev <nets>  <values>                                                                               
* --------------------------                                                                         
I1 n1 0        50uA                                                                                  
V1 vp 0        1.3V                                                                                  
V2 vp n2       0.71005V                                                                              
M1 n1 n1 n3 vp pmos w=100u l=3u                                                                      
M2 n2 n1 n4 vp pmos w=100u l=3u                                                                      
R1 vp n3       3kR                                                                                   
R2 vp n4       3kR  

SPICE Simulations[edit]

n1 = 0.5899
n2 = 0.5899
n3 = 1.15
n4 = 1.15
v1#branch = -50.0
v2#branch = -50.0
(v2#branch/v1#branch) = 1

Operating Point Analysis[edit]

device m2          m1                                                                               
model  pmos        pmos                                                                             
gm     442.69 uS   442.69 uS                                                                        
rds    944.9  kR   944.9  kR                                                                        
id     50.0   uA   50.0   uA                                                                        
vgs    0.5600 V    0.5600 V                                                                         
vds    0.5600 V    0.5600 V                                                                         
vth    0.3689 V    0.3689 V                                                                         
vdsat  0.2036 V    0.2036 V 

DC Analysis (Sweep)[edit]


  • The absolute minimum voltage needed for the mirror to be in the saturation region is it's Vdsat (roughly a Veff) plus the drop across the source resistor at the nominal 50uA mirror current i.e:
Vmin_abs = 0.2036 + 0.150 > 0.3536 V
  • However in practice the current mirror requires at least a 0.45V load voltage to be operational with its maximum Rout (this can be seen from the plot above where the slope is linear).
  • Error Measurement: Variation of 49.7949uA to 50.1906uA over a linear operating range of 0.85 to 0. This is equivalent to an error of 0.3958uA or 0.7915% relative to our current reference.

Figures of Merit[edit]

Output Resistance Rout: 2.1478MΩ (measured from 0.85 to 0V linear range)

Compliance Voltage: 0.45V (relative from VDD)

In summary,

Current Mirrors Performance Summary
Topology Vmin (V) Compliance Voltage (V) r_out (kΩ) Current Consumption (uA) Area (um^2)
Simple PMOS 0.225 0.35 852.78 50 200
PMOS Source Degenerated 0.3536 0.45 2148 50 200 + 2 x A_res