Low power receiver with equalization circuit, communication unit and method therefor
A low power receiver having a feedforward equalization, FFE, based continuous time linear equalizer, CTLE. The FFE CTLE comprises: an input for receiving an input signal; a main first path operably coupled to the input and comprising a source-follower transistor arranged to apply a scaling factor to the received input signal; a second path operably coupled to the input and comprising a delay arranged to apply a delay to the received input signal and a common source transistor common source transistor arranged to apply a scaling factor to the received delayed input signal, wherein the source-follower transistor and the common source, CS, transistor are connected as a single SF-CS stage whose output is arranged to subtract the output of the common source transistor from an output of the source-follower transistor.
1. A low power receiver having a feedforward equalization, FFE, based continuous time linear equalizer, CTLE, wherein the FFE CTLE comprises:
an input for receiving an input signal;
a main first path operably coupled to the input and comprising a source-follower, SF, transistor arranged to apply a scaling factor to the received input signal; and
a second path operably coupled to the input and comprising a delay arranged to apply a delay to the received input signal and a common source transistor arranged to apply a scaling factor to the received delayed input signal, wherein the source-follower transistor and the common source, CS, transistor are connected as a single SF-CS stage whose output is arranged to subtract the output of the common source transistor from an output of the source-follower transistor.
2. The low power receiver of claim 1 , wherein the single SF-CS stage is configured to provide at least one of: a variable gain control to be applied to an equalized version of the received input signal; a buffer to an equalized version of the received input signal.
3. The low power receiver of claim 1 , wherein the CS transistor is connected to the second path via a low pass inductor-capacitor (LC) filter arranged to provide the delay and the received delayed input signal is subtracted from the first source-follower transistor signal creating suppressed low-frequency content and positive gain at higher-frequencies at the output of the common source transistor.
4. The low power receiver of claim 1 , wherein the delay line comprises a ‘T’ circuit comprised of a first series inductor connecting an input port to an intermediate port, a shunt capacitance connecting the intermediate port to ground and a second series inductor connecting the intermediate port to an output port, such that an input capacitance of the CTLE circuit is at least partially provided by the shunt capacitance.
5. The low power receiver of claim 1 , wherein the delay line comprises a differential delay line that is coupled to a second common source transistor.
6. The low power receiver of claim 5 , wherein:
the input for receiving an input signal comprises a first positive input and a second negative input;
the main first path comprises a first positive main path operably coupled to the first positive input and comprising a first source-follower, SF, transistor arranged to apply a first scaling factor to the received input signal and comprises a second negative main path operably coupled to the second negative input and comprising a second source-follower, SF, transistor arranged to apply a second scaling factor to the received input signal;
and the second path comprises a first positive second path operably coupled to the first positive input and comprising a delay arranged to delay the received input signal and a first common source, CS, transistor arranged to apply a third scaling factor to the received delayed input signal comprising a first common source, CS, transistor arranged to apply a scaling factor to the received input signal from the first positive input and comprises a second negative second path operably coupled to the second negative input and comprising a second common source, CS, transistor arranged to apply a scaling factor to the received input signal from the second negative input; and
wherein the first SF transistor and the first CS transistor are connected as a single SF-CS stage whose output is arranged to subtract the output of the first CS transistor from an output of the first SF transistor and produce a CTLE positive output signal and the second SF transistor and the second CS transistor are connected as a second single SF-CS stage whose output is arranged to subtract the output of the second CS transistor from an output of the second SF transistor and produce a CTLE negative output signal.
7. The low power receiver of claim 6 , wherein the CTLE positive output signal is input to a first variable gain amplifier stage and the CTLE negative output signal is input to a second variable gain amplifier stage.
8. The low power receiver of claim 7 , wherein the first variable gain amplifier stage and second variable gain amplifier stage are implemented using passive variable resistors at the respective CTLE positive output and CTLE negative output.
9. The low power receiver of claim 6 , wherein a combined signal from the CTLE positive output signal and the CTLE negative output signal is configured to provide: a low frequency destructive signal component, a differential high frequency constructive signal component and a common mode high frequency destructive signal component at the output of the FFE CTLE.
10. The low power receiver of claim 1 , further comprising a reference degenerated diode coupled to the first source-follower transistor and the second common source transistor arranged to provide a stable bias voltage and the same source current to the source-follower transistor and common source transistor of the FFE CTLE.
11. A method for equalizing a received frequency signal, the receiver having a feedforward equalization, FFE, based continuous time linear equalizer, CTLE, wherein the method comprises:
receiving an input signal;
applying a scaling factor to the received input signal in a main first path by a source-follower, SF, transistor of the FFE CTLE;
applying a delay to the received input signal in a second path of the FFE CTLE;
applying a scaling factor to the received delayed input signal in the second path by a common source, CS, transistor, wherein the SF transistor and the CS transistor are connected as a single SF-CS stage; and
subtracting an output of the CS transistor from an output of the SF transistor.
12. The method for equalizing a received frequency signal of claim 11 , further comprising configuring the single SF-CS stage to provide a variable gain control to be applied to an equalized version of the received input signal.
13. The method for equalizing a received frequency signal of claim 11 , further comprising configuring the single SF-CS stage to provide a buffer to an equalized version of the received input signal.
14. The method for equalizing a received frequency signal of claim 11 , further comprising connecting the CS transistor to the second path via a low pass inductor-capacitor (LC) filter that provides the delay, and subtracting the output of the CS transistor from the output of the SF transistor comprises creating suppressed low-frequency content and positive gain at higher-frequencies.
15. The method for equalizing a received frequency signal of claim 11 , wherein the delay line comprises a differential delay line that is coupled to a second common source transistor.
16. The method for equalizing a received frequency signal of claim 15 , further comprising configuring the single SF-CS stage the combined signal from the source-follower transistor output of the FFE CTLE main path and the second common source transistor and differentially delayed second common source transistor output of the FFE CTLE second path to provide: a low frequency destructive signal component, a differential high frequency constructive signal component and a common mode high frequency destructive signal component at the output of the FFE CTLE.
17. A communication unit comprising a low power receiver having a feedforward equalization, FFE, based continuous time linear equalizer, CTLE, wherein the FFE CTLE comprises:
an input for receiving an input signal;
a main first path operably coupled to the input and comprising a source-follower, SF, transistor arranged to apply a scaling factor to the received input signal;
a second path operably coupled to the input and comprising a delay arranged to apply a delay to the received input signal and a common source transistor arranged to apply a scaling factor to the received delayed input signal, wherein the source-follower transistor and the common source, CS, transistor are connected as a single SF-CS stage whose output is arranged to subtract the output of the common source transistor from an output of the source-follower transistor.
18. The communication unit of claim 17 , wherein the single SF-CS stage is configured to provide at least one of: a variable gain control to be applied to an equalized version of the received input signal; a buffer to an equalized version of the received input signal.
19. The communication unit of claim 17 , wherein the delay line comprises a differential delay line that is coupled to a second common source transistor.
20. The communication unit of claim 19 , wherein:
the input for receiving an input signal comprises a first positive input and a second negative input;
the main first path comprises a first positive main path operably coupled to the first positive input and comprising a first source-follower, SF, transistor arranged to apply a first scaling factor to the received input signal and comprises a second negative main path operably coupled to the second negative input and comprising a second source-follower, SF, transistor arranged to apply a second scaling factor to the received input signal;
and the second path comprises a first positive second path operably coupled to the first positive input and comprising a delay arranged to delay the received input signal and a first common source, CS, transistor arranged to apply a third scaling factor to the received delayed input signal comprising a first common source, CS, transistor arranged to apply a scaling factor to the received input signal from the first positive input and comprises a second negative second path operably coupled to the second negative input and comprising a second common source, CS, transistor arranged to apply a scaling factor to the received input signal from the second negative input;
wherein the first SF transistor and the first CS transistor are connected as a single SF-CS stage whose output is arranged to subtract the output of the first CS transistor from an output of the first SF transistor and produce a CTLE positive output signal and the second SF transistor and the second CS transistor are connected as a second single SF-CS stage whose output is arranged to subtract the output of the second CS transistor from an output of the second SF transistor and produce a CTLE negative output signal.