[ibis-macro] Re: Jitter Bird Graphic, and Backchannel Presentation
- From: <fangyi_rao@xxxxxxxxxxx>
- To: <msteinb@xxxxxxxxxx>, <ibis-macro@xxxxxxxxxxxxx>
- Date: Sun, 22 May 2011 18:54:31 -0600
Hi, Mike;
Thanks for the answers. Noise at the Rx output node, Vout, is determined by
noise at the Rx positive input node, Vin_p, noise at the Rx negative input
node, Vin_n, transfer function from Vin_p to Vout, XF_p, and transfer function
from Vin_n to Vout, XF_n, as
Vout = XF_p*Vin_p + XF_n*Vin_n
Can you further clarify how noise powers of <Vin_p^2> and <Vin_n^2> and
correlation function <Vin_p*Vin_n> are defined in terms of Rx_Noise_Pad?
Fangyi
From: ibis-macro-bounce@xxxxxxxxxxxxx [mailto:ibis-macro-bounce@xxxxxxxxxxxxx]
On Behalf Of Mike Steinberger
Sent: Thursday, May 12, 2011 11:03 AM
To: ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Re: Jitter Bird Graphic, and Backchannel Presentation
Fangyi-
Thanks for the questions. Answers inserted below.
Mike S.
On 05/11/2011 03:20 PM, fangyi_rao@xxxxxxxxxxx<mailto:fangyi_rao@xxxxxxxxxxx>
wrote:
Hi, Walter;
Thanks for the graphs. I have two questions:
Noise "Rx_Noise_Pad" is injected into the analog circuit. What is the impedance
of the noise source? How is the noise source connected to the circuit? Can you
provide a SPICE netlist so that this parameter is unambiguously defined?
The word "injected" is not doing you any favors. Rx_Noise_Pad is a noise
voltage _measured_ at the circuit node which is the input to the receive
amplifier.
There may be a noise injection process; and if there is, its goal is create
conditions which result in a specific noise voltage measured at the input to
the receiver amplifier. For example, the noise injection process could be a
current source driving current into the input of the receiver. If the goal of
that current source is to create a voltage Vn at the receiver input, the input
impedance of the receiver is Zr (approximately equal to Z0=50ohms) and the
source impedance of the interconnect network is Zs (also approximately equal to
Z0) at the input to the receiver, then the current from a current source
injecting into that circuit node should be
In = Vn/(Zr||Zs) = Vn/((Zr*Zs)/(Zr+Zs))
The fact of the matter is that in many SPICE simulations, the noise is actually
inserted in the transistor models, and Rx_Noise_Pad is the noise voltage that
_would_ be injected into the input in order to produce the output noise voltage
that was _actually_ produced by the transistor internal to the circuit. This is
the whole concept of a noise figure http://en.wikipedia.org/wiki/Noise_figure -
very familiar to microwave circuit designers and communications analysts, but
otherwise requiring some time and effort to get used to.
Since parameters Rx_DCD, Rx_RJ and Rx_SJ are jitters external to receiver as
stated in the BIRD, how do Rx model developers know their values? Similarly,
how do Rx model developers know the value of Rx_Noise_Pad which is injected to
the Rx analog circuit?
This is actually two different questions with two different answers.
2a. Rx_DCD, Rx_RJ and Rx_SJ represent the effect of processes such as power
supply noise that are external to the receiver. As such, the model developer
may or may not know their values for a given system or application. For
example, the vendor could specify a maximum tolerable level of power supply
noise, and the model developer could translate those worst case values into
jitter parameters supplied with the model.
!!!-> In this case, the documentation supplied with the model should clearly
state these worst case conditions. <-!!!
It may also be that the model developer does not have any specific information
from which to calculate these jitter parameters. In that case, "Better to
remain silent and let the World think you a fool than to open your mouth and
remove all doubt."
2b. Rx_Noise_Pad is calculated from the receiver noise figure and input
impedance. These are values that only the circuit designer is sure to have
access to.
Thanks,
Fangyi
From: ibis-macro-bounce@xxxxxxxxxxxxx<mailto:ibis-macro-bounce@xxxxxxxxxxxxx>
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Walter Katz
Sent: Tuesday, May 10, 2011 1:13 PM
To: IBIS-ATM
Subject: [ibis-macro] Jitter Bird Graphic, and Backchannel Presentation
All,
Presentation made to IBIS ATM today.
Walter
Walter Katz
wkatz@xxxxxxxxxx<mailto:wkatz@xxxxxxxxxx>
Phone 303.449-2308
Mobile 720.333-1107
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