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staric
Joined: 26 Sep 2003
Posts: 79
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 19 Jul 2004 11:51 What is the function of the circuit in the picture? |
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This circuit is in analog design. M2 and M3 are always on. What is the function of M2 and M3? Could they improve the performance? And what performance? Thanks
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rfsystem
Joined: 25 Feb 2002
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| 19 Jul 2004 12:19 Re: What is the function of the circuit in the picture? |
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| Put also the dimensions into the schematic. If the two static MOS are long channnel I think it is for limiting rise/fall time without having the capacitive gate load on the switch input. So using minimum at the switch and long channel for the static MOS.
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aProgrammer
Joined: 29 Mar 2001
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| 19 Jul 2004 12:29 Re: What is the function of the circuit in the picture? |
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| this is a complementary cascode configuration.
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staric
Joined: 26 Sep 2003
Posts: 79
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| 19 Jul 2004 14:25 Re: What is the function of the circuit in the picture? |
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| aProgrammer wrote: |
| this is a complementary cascode configuration. |
What is the complementary cascode configuration? Which book is discussed it? Sorry, I have not seen complementary cascode configuration. Thanks.
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barrybear
Joined: 22 Nov 2001
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| 19 Jul 2004 15:24 Re: What is the function of the circuit in the picture? |
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A complimentry output stage. Just as a matter of intrest the vcc power supply points . Is one of them positive and the other a negative voltage. If this is the case then the output stage would provide a near faithfull duplication of the input but with a great deal of power.
Barrybear
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dumbfrog
Joined: 17 Jul 2004
Posts: 191
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| 20 Jul 2004 18:52 Re: What is the function of the circuit in the picture? |
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handle higher voltage supply
ie. a 0.25um process usually operates at 2.5V, but with the cascode scheme, it can operate at 3.3V or higher
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rfsystem
Joined: 25 Feb 2002
Posts: 811
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| 20 Jul 2004 22:43 Re: What is the function of the circuit in the picture? |
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| I do not think it is a complementary output stage because the output voltage range where the output impedance is high is relative small. Could you answer what type of input signal is normally applied?
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eternal_nan
Joined: 10 Mar 2003
Posts: 158
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| 21 Jul 2004 3:34 What is the function of the circuit in the picture? |
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| I agree with rfsystem, it would be stupid to use this circuit as an output stage; most likely it is just an inverter with tweeked rising-edge and falling-edge propagation delays...
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sunking
Joined: 25 May 2004
Posts: 914
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| 21 Jul 2004 8:07 Re: What is the function of the circuit in the picture? |
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| them increase the output resistor
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flyankh
Joined: 16 Feb 2004
Posts: 94
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| 21 Jul 2004 10:34 Re: What is the function of the circuit in the picture? |
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Hi
I ask one of our analog designer to simulate the circuit,and an normal inverter was simulated too as the contrast to it.
The red line is the normal inverter's output,the green is this circuit's,the third one is the input signal.
Now can you find the differences?
[/img]
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jyq_analog
Joined: 10 Dec 2003
Posts: 17
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| 21 Jul 2004 12:46 What is the function of the circuit in the picture? |
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staric wrote <This circuit is in analog design. M2 and M3 are always on. What is the function of M2 and M3? Could they improve the performance? And what performance? >
if M2 and M3 are always on,the circuit is a inverter.
M2 and M3 reduce the output voltage range.
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totoro
Joined: 27 Jun 2004
Posts: 86
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| 22 Jul 2004 16:47 Re: What is the function of the circuit in the picture? |
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| jyq_analog wrote: |
staric wrote <This circuit is in analog design. M2 and M3 are always on. What is the function of M2 and M3? Could they improve the performance? And what performance? >
if M2 and M3 are always on,the circuit is a inverter.
M2 and M3 reduce the output voltage range. |
M2 and M3 will not reduce the output valtage swing.
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totoro
Joined: 27 Jun 2004
Posts: 86
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| 22 Jul 2004 16:59 Re: What is the function of the circuit in the picture? |
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From my point of view,
It just acts as a invertor.
M2 & M3 are used to prevent the input signal from coupling to the output.
Charge feedthrough will occur due to capacitors Cgd if M2 and M3 do not exist.
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rickhsu
Joined: 31 Jan 2004
Posts: 20
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| 13 Aug 2004 2:27 Re: What is the function of the circuit in the picture? |
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In my view.
It may have 2 purpose
1.reduce power waste during power on.
or
2.reduce di/dt of the circuit
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santhoshv78
Joined: 22 Jun 2004
Posts: 72
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| 13 Aug 2004 3:12 Re: What is the function of the circuit in the picture? |
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I agree with totoro...
This technique is mainly used to avoid the charge feedthrough...
You can see the result in the waveform simulated. red waveform without the M2 and M3 has more glitch at the transition point but not the green waveform (with M2 and M3).
This is mainly used in current steering DAC design( just below the switch) to reduce the glitch energy.
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rickhsu
Joined: 31 Jan 2004
Posts: 20
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| 17 Aug 2004 2:55 Re: What is the function of the circuit in the picture? |
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IF try simulate different cload from small to large.
the simulation will tell.
1. clk feedthrouth by cgd,not the reson,why dont you just add to cload
2. charge injection by channel ,YES.It is different but....
if the circuit is mainly digital output...accurate maynot a mainly issue
if the circuit is mainly analog,the bias will not choose vdd/vss,it can choose a better point for Rout or distortion consideration in all signal swing
1.the peak di/dt is different
2.current inject to substate is different
3.the noise to power line is different
4.the speed/power is different
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rajath
Joined: 13 Aug 2004
Posts: 43
Helped: 2
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| 17 Aug 2004 8:36 Re: What is the function of the circuit in the picture? |
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Glitch is more of a reliability issue than accuracy. But you are right in divining that the circuit is not used in analog applications. Else the CG transistor switching from triode to active region will introduce quiet a bit of non-linearity. Even I agree that the extra CG transistors just provide a low impedance node for the charge injection, thus isolating the output.
ps: CG=common gate
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airace
Joined: 17 Sep 2002
Posts: 97
Location: Deep in a chip
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| 17 Aug 2004 9:39 Re: What is the function of the circuit in the picture? |
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This is nothing but an invertor and is common in I/O circuit design.
Primarily used for situations where the X'tors are LV devices and you want to operate of higher power supply.
This is primarily to handle VDSmax violations.
Regards,
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guilinwxb
Joined: 19 Apr 2008
Posts: 16
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| 12 Dec 2008 16:44 Re: What is the function of the circuit in the picture? |
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Hi, all
This question is just like my question. There is a cascode feedback amp with a complementary transconductance stage as illustrated in the Fig, it is used for better tradeoff between noise performance and linearity at low power consumption.
Can anyone tell me about the operation principle of this circuit, or any link to talk about it ?
Thanks a lot!
[img]
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leo_o2
Joined: 03 Sep 2004
Posts: 356
Helped: 22
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| 14 Dec 2008 4:24 What is the function of the circuit in the picture? |
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I think the two circuits are different. The first one should be a inverter with limited switching current. In some application, if the voltage of "IN " changes very slowly, a big current will flow in the inverter during transition. So the current should be limited.
M2 and M3 with big L/W should behave as resistors.
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