D

#### David Moreno

- Jan 1, 1970

- 0

I'm currently working in a fast switching current mirror to charge

linearly a capacitor. The circuit is a normal current mirror with

a multiplexor attached to the base of the second transistor and a

voltage

generator to switch the current throught it base.

In the simulation I've found that when you rise the frequency (at

50MHz or so)

the current mirror is not fast enought to switch, and a delay appears

that

makes the current throught the capacitor to lower. I'm intriguing in

this

because the transistor that I'm using are known to work up to 5-6GHz,

and the

frecuency of the switching is well below that.

In the practice the results are simply that the current mirrored is

not

the same as the origin current, and the diference increases when you

rise

the frecuency.

And finally the question: Some way to make this work faster or better

the response at high frecuencies ?

Thanks a lot ! =D

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* E:\ALIENFILES\electronica\current mirror\espejo bft93.asc

X§Q1 N003 N003 N001 BFT93

X§Q2 Uc N004 N001 BFT93

C1 Uc 0 47pF

V1 N001 0 5

I1 N003 0 PULSE(0 1mA 0 0.1ns 0.1ns 5ns 10ns)

V2 N002 0 PULSE(0 5 0 0.1ns 0.1ns 5ns 10ns)

S1 N003 N004 N002 0 miswitch

S2 N004 N001 0 N002 miswitch

..inc "E:\ALIENFILES\electronica\spice\bft93.spice"

..tran 240n

..model miswitch SW(Ron=1. Roff=1MEG Vt=2.5V Vh=0 Lser=0 Vser=0)

..ic V(Uc)=0V

..backanno

..end

--------------------------------------------------------------------------------------------

bft93.spice

* Filename: BFT93_SPICE.PRM

* BFT93 SPICE MODEL

* PHILIPS SEMICONDUCTORS

* Date : September 1995

*

* PACKAGE : SOT23 DIE MODEL : BFT93

* 1: COLLECTOR; 2: BASE; 3: EMITTER;

..SUBCKT BFT93 1 2 3

Q1 6 5 7 7 BFT93

* SOT23 parasitic model

Lb 4 5 .4nH

Le 7 8 .83nH

L1 2 4 .35nH

L2 1 6 .17nH

L3 3 8 .35nH

Ccb 4 6 0.071pF

Cbe 4 8 0.002pF

Cce 6 8 0.071pF

* PHILIPS SEMICONDUCTORS Version:

2.0

* Filename: BFT93.PRM Date:

March 1992

*

..MODEL BFT93 PNP

+ IS = 8.35127E-016

+ BF = 4.85648E+001

+ NF = 1.00043E+000

+ VAF = 1.90118E+001

+ IKF = 1.46824E-001

+ ISE = 9.09455E-014

+ NE = 1.74928E+000

+ BR = 1.21832E+001

+ NR = 9.97694E-001

+ VAR = 3.37492E+000

+ IKR = 6.74270E-003

+ ISC = 2.34297E-014

+ NC = 1.44993E+000

+ RB = 1.00000E+001

+ IRB = 1.00000E-006

+ RBM = 1.00000E+001

+ RE = 2.00000E-001

+ RC = 3.80000E+000

+ EG = 1.11000E+000

+ XTI = 3.00000E+000

+ CJE = 1.57034E-012

+ VJE = 6.00000E-001

+ MJE = 3.82204E-001

+ TF = 1.48531E-011

+ XTF = 2.20970E+000

+ VTF = 2.98987E+000

+ ITF = 1.43721E-002

+ CJC = 1.99525E-012

+ VJC = 5.84499E-001

+ MJC = 2.81320E-001

..ENDS

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