# Convert Gigabit to Gigahertz

#### hoyyoth

Joined Mar 21, 2020
217
Dear Team,

May I know the relation between Gigabits and Gigahertz.

Is 1 Gigabit is equal to 1 Gigahertz.

Regards
HARI

#### MrChips

Joined Oct 2, 2009
27,120
Dear Team,

May I know the relation between Gigabits and Gigahertz.

Is 1 Gigabit is equal to 1 Gigahertz.

Regards
HARI
There is no relationship.
giga means ten to the 9th power, i.e. 1,000,000,000

hertz is a unit of frequency. Hence 1GHz = 1,000,000,000 cycles per second

1 Gigabit is 1,000,000,000 bits.

#### hoyyoth

Joined Mar 21, 2020
217
Hi,

Thank you..
For Gigabit Ethernet what is the Nyquist frequecy.
I have seen in many places instead of clock speed people are telling Gigabit,Mbit etc.If there is a way to obtain frequency
from this it is well and good.

Regards
HARI

#### Papabravo

Joined Feb 24, 2006
19,284
Hi,

Thank you..
For Gigabit Ethernet what is the Nyquist frequecy.
I have seen in many places instead of clock speed people are telling Gigabit,Mbit etc.If there is a way to obtain frequency
from this it is well and good.

Regards
HARI
Bits and clocks are not necessarily related to each other. You also have to look at the implementation of the physical layer to understand the relationship between symbols and bits per symbol on the wire. They do crazy stuff to pack bits into symbols.

#### MrChips

Joined Oct 2, 2009
27,120
Ah, Gigabit Ethernet, if that is what you meant.

Gigabit Ethernet refers to transmission rates of 1000Mbit per second. This is not the same as 1GHz because various encoding and modulation schemes are used to pack the data.

#### crutschow

Joined Mar 14, 2008
30,788
For Gigabit Ethernet what is the Nyquist frequecy.
The Nyquist frequency refers to the minimum sampling rate for the highest frequency of a sampled-data analog signal.
Ethernet is not a sampled data signal, it simply transmits a digital signal using a specific protocol, so the question is not answerable.

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#### Ya’akov

Joined Jan 27, 2019
6,561
For a long time, the symbol rate and the bit rate of a data transmission were the same thing. When a telephone modem transmitted data using a 300 baud symbol rate, changing the signal 300 times per second, it was also transmitting data at a (gross) bit rate of 300 bits per second.

Because of the limits physical media impose on maximum symbol rate, various techniques that can take advantage of multiple attributes of the signal (phase, amplitude, and duration), and clever encoding schemes, were developed to make it possible to send more than one bit per symbol.

We have decoupled the baud rates and bit rates in all modern digital communications.

#### hoyyoth

Joined Mar 21, 2020
217
The Nyquist frequency refers to the minimum sampling rate for the highest frequency of a sampled-data analog signal.
Ethernet is not a sampled data signal, it simply transmits a digital signal using a specific protocol, so the question is not answerable.
Hi ,
Thank you.
Ethernet I just took as an example.
My intention is if some says speed in Gigabit I need to know the clock rate

Regards
HARI

#### hoyyoth

Joined Mar 21, 2020
217
Ah, Gigabit Ethernet, if that is what you meant.

Gigabit Ethernet refers to transmission rates of 1000Mbit per second. This is not the same as 1GHz because various encoding and modulation schemes are used to pack the data.
Hi Mrchips,
"Gigabit Ethernet refers to transmission rates of 1000Mbit per second. This is not the same as 1GHz because various encoding and modulation schemes are used to pack the data. " May I know Then what will be the clock rate for this.

Regards
HARI

#### hoyyoth

Joined Mar 21, 2020
217
Dear Team,

I got the answer for my question from the below video of Rick Hartley

In this video what he says is given below

63:33
gigabits as in usually double
63:34
the frequency so an eight gigabit design
63:37
okay operating at about four gigahertz

Regards
HARI

#### Ya’akov

Joined Jan 27, 2019
6,561
There is not one case hePCB, re. The discussion in the video is about signals on a not an Ethernet cable.

#### Deleted member 115935

Joined Dec 31, 1969
0
If in a simple on / off code ( binary )
then there is 2 bit per Hz,

Think of a sine wave, half is up and half is down,

Think of two bits, one '1' and '0' . that looks liek a squared off sine wave !

So if you have say 2 bit per second, alternately 1010101010
then the fundamental frequency would be 1 Hz

Two buts

a) to get a square wave, you need the odd harmonics, at least the 7th

b) as is mentioned above, modern systems dont use "single bit binary" coding
modern coms systems talk in terms of symbols per second,
were a symbol could be multi bits, or multiple values per period...

and one last "gotya"

Things like GbE , use multiple pairs to send the data ,
typically 2 each way,
so with the data spread across the pairs, the bandwidth on each line is halfed for the same data rate.

There is also something called Shannons law

which relates bandwidth to bits per second ,

In truth
there are codding schemes out there that now break this "law", depending how you read the law,
but thats another discussion,,,

#### hoyyoth

Joined Mar 21, 2020
217
There is not one case hePCB, re. The discussion in the video is about signals on a not an Ethernet cable.
Hi

In my previous posts I mentioned ethernet just as an example.
My intention is to get clock frequency when some says my speed is Xgigabits

Regards
HARi

#### Ya’akov

Joined Jan 27, 2019
6,561
Hi

In my previous posts I mentioned ethernet just as an example.
My intention is to get clock frequency when some says my speed is Xgigabits

Regards
HARi
My point is that there is not a general case. The relationship between symbol and bit rates varies depending on the physical medium and encoding.

I explained this above, it hasn't changed.

[EDIT: Grammar fix, number agreement.]

Last edited:

#### eetech00

Joined Jun 8, 2013
3,418
My intention is to get clock frequency when some says my speed is Xgigabits
You need to ask (the person telling you that) that question.

#### michael8

Joined Jan 11, 2015
317
Gigabit Ethernet over copper wiring uses all for pair in full duplex (each pair in both directions at the same time).

https://en.wikipedia.org/wiki/Gigabit_Ethernet#1000BASE-T

So it's 2 bits/symbol * 125 megabaud symbols/pair * 4 pair -> 1000 megabits/second.

It's a bit complex starting with the echo cancellation which allows using each pair in both directions at the same time along with
a lot of coding (the bits aren't sent directly but groups of bits are coded into longer groups and more).

#### hoyyoth

Joined Mar 21, 2020
217
Gigabit Ethernet over copper wiring uses all for pair in full duplex (each pair in both directions at the same time).

https://en.wikipedia.org/wiki/Gigabit_Ethernet#1000BASE-T

So it's 2 bits/symbol * 125 megabaud symbols/pair * 4 pair -> 1000 megabits/second.

It's a bit complex starting with the echo cancellation which allows using each pair in both directions at the same time along with
a lot of coding (the bits aren't sent directly but groups of bits are coded into longer groups and more).
Hi Michael,

Thank you .This is very helpful.

Regards
Hari