Re: FET versus bipolar in MC input cascode

Posted by jcox (A) on January 14, 2002 at 10:38:10

In Reply to: FET versus bipolar in MC input cascode posted by KlausB on January 9, 2002 at 02:46:10:

I can recommend:

Bipolar "Super-Pair" Cascode

               V+      V+
              |       |
              |       Rload
           Isource    |________Vout
              |       |
              |     |/
        Qa    |-----|
           ||/      |\|  Qb
Vcascode---| -       -|
           |\_________|
                      |
	              I_signal (2SK369_Drain)

Baxendall, Electronics Letters
vol 2, 1966, p351
( I haven't seen this article but was referenced in an advanced
circuit design textbook -- which my local library has moved to
storage )

Hawksford, Reduction of Transistor Slope Impedance Dependent
Distortion in Large-Signal Amplifiers
Vol. 36, Number 4 pp. 213 (1988)

Largely forgotten during 70's, rediscovered/reinvented in 90's as
complementary bipolar IC processes and current feedback op amps
became popular

Hawksford's paper analyses circuit, shows near equivalence to
traditional cascode, shows many topological variants with
application to discrete audio amplifier design

Provides nearly 100x improvement in nonlinearity due to Hfe and
collector-base impedance variation over single transistor
( Ccb cancellation gives traditional cascode's speed as well )

In preamp application I would consider super pair in a folded-
cascode arrangement, trading multiplied current for more efficient
use of supply voltage as well as referencing signal to gnd
( admittedly mostly an aesthetic issue with given circuit )

Use high gain(hfe)low noise transistors, Qa Ic ~ 1/2 Qb

Isource could be resistor with > 2.6 V delta

Additionally, in reference to preamp, I would think the implied
design philosophy would require balancing source

noise performance will improve with MC input if series 220R is
reduced or eliminated

cable capacitance and Cgss will resonate with coil inductance in RF
region, R-C snubber across coil could control Q -- should actually
take advantage of this and explicitly design-in input RF filtering
( allowing for recommended coil loading in audio range )

As a professional analog instrumentation designer I cannot
over-emphasize EMI/RFI control at microvolt signal levels;

Shielding
RF bandwidth grounding, 360 degree shield
termination -> phonograph + preamp in a ( iron ) box?

Filtering
lossy ferrite common-mode beads, RF/feedthru caps on inputs,
internal low pass at intermediate stages ( RF cap bypass Rload
to (AC) ground or you will be feeding local AM radio into op amp
input )

I would also expect the super-pair circuit would interest minimalist
current DAC designers

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Follow Ups Full Thread

Topic - FET versus bipolar in MC input cascode - KlausB 02:46:10 01/09/02 (33)

Re: FET versus bipolar in MC input cascode - jcox 10:38:10 01/14/02 (0)

Re: FET versus bipolar in MC input cascode - Terry Demol 00:01:09 01/10/02 (3)

Re: FET versus bipolar in MC input cascode - KlausB 09:55:34 01/10/02 (2)

Re: FET versus bipolar in MC input cascode - Terry Demol 18:00:10 01/10/02 (1)

MAT-transistors are MATched devices, right - groman 18:10:02 01/10/02 (0)

Re: FET versus bipolar in MC input cascode - Thorsten 10:02:44 01/09/02 (5)

Re: FET versus bipolar in MC input cascode - capslock 14:02:00 01/09/02 (4)

Re: FET versus bipolar in MC input cascode - Thorsten 15:36:50 01/09/02 (0)

cascode lin for dV over load, but makes slower circuit - groman 14:08:20 01/09/02 (2)

I will stick around!, John Curl. I often know what I am talking about. - groman 15:46:38 01/13/02 (0)

Re: cascode lin for dV over load, but makes slower circuit - john curl 18:10:15 01/11/02 (0)

Idss - PhilH 05:50:04 01/09/02 (1)

Re: Idss - KlausB 09:14:29 01/09/02 (0)

I could explain. Schematic, thank you. - groman 05:27:15 01/09/02 (8)

Re: I could explain. Schematic, thank you. - KlausB 09:16:03 01/09/02 (7)

Very Great Site, I Enjoy it!!!!!! - groman 09:50:32 01/09/02 (5)

Thanks a lot ! - KlausB 12:13:56 01/09/02 (4)

I like to make somebody glad. Then my life is worth something. - groman 12:19:57 01/09/02 (3)

Re: I like to make somebody glad. Then my life is worth something. - PhilH 19:30:51 01/09/02 (2)

Re: loveletters are written in sand - groman 03:40:25 01/10/02 (0)

talk to me with mIRC - groman 20:25:15 01/09/02 (0)

many Thanks KlausB, will go there - groman 09:22:13 01/09/02 (0)

Rule: BIPOLAR. Other options are inferior, as with todays semiconductors. - groman 05:15:30 01/09/02 (1)

Was written only as answer to Headline. - groman 05:21:48 01/09/02 (0)

Re: FET versus bipolar in MC input cascode - capslock 05:06:33 01/09/02 (6)

Re: FET versus bipolar in MC input cascode - KlausB 09:19:44 01/09/02 (5)

Re: FET versus bipolar in MC input cascode - capslock 13:51:58 01/09/02 (4)

Re: FET versus bipolar in MC input cascode - KlausB 05:43:47 01/11/02 (3)

small corrective voltage, you mean will dist? - groman 07:20:23 01/11/02 (2)

Glad you did not leave the asylum ! - KlausB 15:07:54 01/11/02 (1)

Re: Glad you did not leave the asylum ! - groman 15:07:53 01/12/02 (0)

Re: FET versus bipolar in MC input cascode - Elso Kwak 03:05:56 01/09/02 (1)

Re: FET versus bipolar in MC input cascode - KlausB 03:56:55 01/09/02 (0)

Follow Ups

Re: FET versus bipolar in MC input cascode - jcox 10:38:10 01/14/02 (0)

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