These are current sources rather than mirrors. A current reference and mirror circuit is usually generating the bias levels.
A simple think to do is to include inside the amplifier the complete mirror for biasing you amplifier current sources. Then distribute currents from outside going to the amplifier mirrors. This way you know you have to match transistors that are physically close and not on opposite ends of the chip.
@Junus2012
sutapanaki is correct. The picture from you first post is from Razavi. While M3-M4 and M7-M8 serve as casodes, let's say they can be biased with more or less controlled voltage. However, M5-M6 and M9-M10 are current sources and if you want to control the current in them you bias them using current mirrors, for example, as you drew it in your picture.
See Baker (https://cmosedu.com/cmos1/book.htm), he always control currents in branches.
Regarding IEEE papers, sometimes there is shown more or less. As sutapanaki metioned, very often authors want to concentrate on the core circuit.
While VB1 and VB2 is a biasing voltage for the cascode transistors M3,M4,M7 and M8 and it is not critical, but Vb3 and VB4 are biasing the upper and down mirror, if the transistors generating these voltages are not matched to the transistor in the ampliifer this will lead to mismatching in the current.
My question, when you design such circuit, do you consider to match the biasing circuit to the core circuit,
Thank you friends,
I have also seen this slide, he is matchiung the current mirror from the biasing circuit to the ampliifer core
Which follow your suggestion,
View attachment 159194
Regarding Baker, he always writes or it is on pictures that PMOS and NMOS are identical and some of them are just multiplication (so also matched).
Source: https://payhip.com/b/5Srt ("Preview" button in top right corner)
"All the other NMOS transistors are identical. The same is true for PMOS devices." Just M3 is doubled to have twice the current that M8.
Generally, matching is extremely important in analog IC design. In that way you control currents and voltages in a circuit.
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I do not believe. Somebody put Baker in Google Drive: **broken link removed** . See page 1.100:
PMOS are 100/2
NMOS are 50/2
Other dimensions are shown in the picture.
yes I believe that matching is important for layout, no doubt about it, but I think you are referring to another kind of matching in your explanation
What exactly matching do you think of? How can I help you?
In your original Razavi folded cascode opamp following are cricital and must be matched:
- M1-M2
- M5-M6 with other diode-connected NMOS that provides bias voltage and hence set the desired currents in M5 and M6
- M9-M10 with other diode-connected PMOS that provides bias voltage and hence set the desired currents in M9 and M10
M3-M4 and M7-M8 are cascodes so you do not set currents in them by Vb1, Vb2. Currents are set by M5-M6 and M9-M10, respectively.
Dear T4_V
Anyway, Mr. Suta also confirmed it, and I am going to match the grouped transistors, means biasing mirror has to be matched in the same matching array of the core amplifier transistors,
Also as Suta mentioned, we can supply the current of these mirrors by means of copy of the reference current in the circuit
View attachment 159232
Yes, exactly. You want to match:
- PMOS Mx1, M9, M10
- PMOS Mx2, M7, M8
- NMOS Mx3, M3, M4
- NMOS Mx4, M5, M6
Even if core and bias circuits are in separate blocks, one should think of them as unity.
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