I am working on a bluetooth module for streaming audio signals. Audio signals coming from audio jacks are single ended,but datasheet of module has mentioned that differential audio signals are recommended. is there any way to convert single ended audio signal to differential one. Through internet search, I found this schematic:
Is this method valid for conversion?
It is possible that I have misunderstood the requirement - but if not...
The vintage way of getting differential audio signals from a single-ended input consisted of merely using an audio frequency transformer, usually a 2 pin input 3 pin output little thing, with a 1:1 turns ratio.
The single-ended signal feeds the transformer input, and the output side is a differential signal pair you can bias to wherever you need it to be - connect the middle pin of the output to ground, and the differential signal is ground-referenced.
In addition, a turns ratio other than 1:1 allows impedance matching / voltage gain if desired.
This is an extended comment to address what I believe is an important distinction to make - the distinction between a balanced output and a differential output.
According to the link provided by Phil Frost, we have:
A good, accurate definition is "A balanced circuit is a two-conductor circuit in which both conductors and all circuits connected to them have the same impedance with respect to ground and to all other conductors...
Thus, this would be an example of a balanced output:
simulate this circuit – Schematic created using CircuitLab
Though the output is balanced according to the above definition, it is not differential.
For the output to be differential, we must have \$V^+_{out} = -V^-_{out}\$
But, for the circuit above, we have (for open circuit condition) \$V^+_{out} = V_{oc} \$, and \$V^-_{out} = 0\$
This is an example of a differential output:
Note that this is not a balanced output since the impedance to ground for the positive output node is \$600\Omega\$ while the impedance to ground for the negative output node is \$0\Omega\$.
However, for both circuits, the open circuit output voltage is \$V^+_{out} - V^-_{out} = V_{oc}\$ and the output impedance is \$600\Omega\$.
Finally, an example of a balanced and differential output:
As to the OP's question:
is there any way to convert single ended audio signal to differential one
The answer is yes, of course there is and certainly, as Anido Ghosh answers, a 1:1 audio transformer will give you both a balanced and differential output as well as isolation which may or may not be useful.
As other answers have pointed out, you can can also convert to differential only or balanced only.
Whether you actually need both, one or the other, or neither is a matter for experiment to decide.
Use an op-amp configured as a unity gain inverter. Feed its input from the audio jack. The output from the op-amp is an inverted version of the signal from the audio jack and suitable for devices requiring differential inputs. +input = audio jack signal, -input is o/p from op-amp inverter.
In all likelihood, you'll probably find that the Bluetooth module works just fine with a single-ended input.
Here is a diagram from the design of high-performance balanced audio interfaces by Bill Whitlock & Rod Elliott - it shows several methods:
Note the top left circuit. What I'm proposing is a cut-down version of this. The non-inverting stage I'm proposing can be removed leaving only the inverting op-amp stage. The diagram does show RS1 and RS2 for when impedance balancing is required and I'm not saying you don't need these components but in many circumstances they are not needed, particularly in the application in the question.
The schematic in your question does not convert to a differential signal. It is merely a circuit to bias two microphones (likely, electret microphones).
The advantage to a differential signal is increased noise immunity, especially over long runs. You may not require any additional noise immunity, and unless you can make the single-ended runs shorter by converting to differential somewhere, you aren't going to get it anyway.
To connect your single-ended audio signal to the differential input is easy: connect the inverting input of the differential input to ground, and the ground-referenced audio signal to the non-inverting input.
To make a differential signal, you need two signal lines with equal impedances that carry the signal in their difference. What you don't need is an inverted copy of your signal. There are a lot of ways to accomplish that, but with modern electronics, at audio frequencies, a common approach which works well enough while remaining quite simple is this:
This is from an article, Design of High-Performance Balanced Audio Interfaces, by Bill Whitlock & Rod Elliott. Notice there's no inverting of the signal. R2, R3, R4, and C1 are the balancing. It's important that R2 and R3 are exactly the same value: use 0.1% tolerance resistors.
