Devices and methods capable of addressing filter responses are disclosed. For example, a method for compensating a first low-pass filter and a second low-pass filter is disclosed. The method includes injecting a reference tone fR and a cutoff tone fC into the first low-pass filter, and measuring respective filter responses of the reference tone fR and the cutoff tone fC while changing capacitor codes that control a cutoff frequency of the first low-pass filter until a first capacitor code ICODE is determined that most accurately causes the first low-pass filter to utilize a desired cutoff frequency f0, performing a similar operation for the second low-pass filter until a second capacitor code QCODE is determined, and calibrating for mismatch between the first low-pass filter and the second low-pass filter.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A method for compensating for non-idealities in a filter circuit that includes programmable filter circuitry including a first low-pass filter and a second low-pass filter both having a common desired cutoff frequency f 0 , the method comprising: for a first desired bandwidth BW 0 corresponding to the common desired cutoff frequency f 0 , injecting a reference tone IR and a cutoff tone fC into the first low-pass filter, and measuring respective filter responses of the reference tone fR and the cutoff tone fC while changing capacitor codes that control a cutoff frequency f 0 -I of the first low-pass filter until a first capacitor code ICODE is determined that causes the first low-pass filter to match the desired cutoff frequency f 0 as close as possible given an available resolution of the capacitor codes; for the first desired bandwidth BW 0 , injecting the reference tone fR and the cutoff tone fC into the second low-pass filter, and measuring respective filter responses of the reference tone fR and the cutoff tone fC while changing capacitor codes that control a cutoff frequency f 0 -Q of the second low-pass filter until a second capacitor code QCODE is determined that causes the second low-pass filter to match the desired cutoff frequency f 0 as close as possible given the available resolution of the capacitor codes; and further calibrating for mismatch between the first low-pass filter and the second low-pass filter for one or more additional bandwidths greater than the first desired bandwidth BW 0 .
2. The method of claim 1 , wherein the one or more additional bandwidths include a second desired bandwidth BW 1 , where BW 1 =N×BW 0 , where N is a positive integer greater than 1.
3. The method of claim 2 , wherein calibrating for mismatch between the first low-pass filter and the second low-pass filter includes: for a respective second cutoff frequency f 1 , where f 1 =(N×f 0 )+Δf, where Δf is a cutoff frequency offset for the second desired bandwidth BW 1 : determining a capacitor code offsets ΔI OFFSET and ΔQ OFFSET ; adding the capacitor code offset ΔI OFFSET to the first capacitor code I CODE to produce a first compensated capacitor code I C-CODE ; and adding the capacitor code offset ΔQ OFFSET to the second capacitor code Q CODE to produce a second compensated capacitor code Q C-CODE , wherein the second cutoff frequency f 1 =(N×f 0 )+Δf, where Δf is a cutoff frequency offset for the second desired bandwidth BW 1 .
4. The method of claim 3 , wherein BW 0 =20 MHz, BW 1 =40 MHz, f 0 =8.75 MHz, f 1 =18.75 MHz, and Δf=1.25 MHz; or wherein BW 0 =20 MHz, BW 1 =80 MHz, f 0 =8.75 MHz, f 1 =38.75 MHz, and Δf=3.75 MHz.
5. The method of claim 3 , wherein calibrating for mismatch between the first low-pass filter and the second low-pass filter further includes: determining a fractional capacitor code CI FRAC corresponding to the first desired bandwidth BW 0 , the fractional capacitor code CI FRAC being a value that lies between two consecutive capacitor codes [I CODE , I CODE+1 ], and that ideally corresponds to both a zero phase difference and a zero power difference between the first low-pass filter and the second low-pass filter; and using the fractional capacitor code CI FRAC to determine the capacitor code offsets ΔI OFFSET and ΔQ OFFSET .
6. The method of claim 5 , wherein determining the fractional capacitor code CI FRAC includes: interpolating a line using a plurality of points with each point having a first dimension being a combined I-Q capacitor code [I CODE , Q CODE ], and a second dimension being a respective measured phase offset between the first low-pass filter and the second low-pass filter using a respective combined I-Q capacitor code; and selecting a combined I-Q capacitor code value that corresponds to a substantially zero phase difference between the first low-pass filter and the second low-pass filter.
7. The method of claim 5 , wherein using the fractional capacitor code C FRAC to determine the capacitor code offset ΔI OFFSET and ΔQ OFFSET includes: rounding the fractional capacitor code CI FRAC to a nearest integer to produce the capacitor code offset ΔI OFFSET and ΔQ OFFSET ; adding the capacitor code offset ΔI OFFSET to the first capacitor code I CODE to produce the first compensated capacitor code I C-CODE ; and adding the capacitor code offset ΔQ OFFSET to the second capacitor code Q CODE to produce the second compensated capacitor code Q C-CODE .
8. The method of claim 7 , wherein using the fractional capacitor code CI FRAC to determine the capacitor code offsets ΔI OFFSET and ΔQ OFFSET includes: rounding to the nearest integer a scaled value=[(1+αΔfc)*ΔC FRAC ] to produce the capacitor code offsets ΔI OFFSET and ΔQ OFFSET , where ΔC FRAC is a difference between the first capacitor code CI FRAC and the second capacitor code Q CODE , a is a scaling factor derived from empirical data, and Δfc is a capacitor code difference corresponding to the cutoff frequency offset Δf; adding the capacitor code offset ΔI OFFSET to the first capacitor code I CODE to produce the first compensated capacitor code I C-CODE ; and adding the capacitor code offset ΔQ OFFSET to the second capacitor code Q CODE to produce the second compensated capacitor code Q C-CODE .
9. The method of claim 8 , further comprising: applying the first compensated capacitor code I C-CODE to the first low-pass filter; and applying the second compensated capacitor code Q C-CODE to the second low-pass filter.
10. A wirelessly operating device that operates according to the method of claim 1 .
11. A device for compensating for non-idealities in a filter circuit that includes programmable filter circuitry including a first low-pass filter and a second low-pass filter both having a common desired cutoff frequency f 0 corresponding to a first desired bandwidth BW 0 , the device comprising: code search circuitry that controls the first low-pass filter and the second low-pass filter; tone generation circuitry that injects a reference tone f R and a cutoff tone f C into both the first low-pass filter and the second low-pass filter, measurement circuitry that: (1) measures respective filter responses of the reference tone f R and the cutoff tone f C while the code search circuitry changes capacitor codes that control a cutoff frequency f 0-1 of the first low-pass filter until a first capacitor code I CODE is determined that causes the first low-pass filter to match the desired cutoff frequency f 0 as close as possible given an available resolution of the capacitor codes; and (2) measures respective filter responses of the reference tone f R and the cutoff tone f C while the code search circuitry changes capacitor codes that control a cutoff frequency f 0-Q of the second low-pass filter until a second capacitor code Q CODE is determined that causes the second low-pass filter to match the desired cutoff frequency f 0 as close as possible given the available resolution of the capacitor codes; and calibration circuitry configured to calibrate for mismatch between the first low-pass filter and the second low-pass filter for one or more additional bandwidths greater than a first desired bandwidth BW 0 of the desired cutoff frequency f 0 .
12. The device of claim 11 , wherein each of the one or more additional bandwidths include a second desired bandwidth BW 1 , where BW 1 =N×BW 0 , where N is a positive integer greater than 1.
13. The device of claim 12 , wherein the calibration circuitry is further configured to: for a respective second cutoff frequency f 1 for the second bandwidth BW 1 , determine a capacitor code offsets ΔI OFFSET and ΔQ OFFSET ; add the capacitor code offset ΔI OFFSET to the first capacitor code I CODE to produce a first compensated capacitor code I C-CODE ; and add the capacitor code offset ΔQ OFFSET to the second capacitor code Q CODE to produce a second compensated capacitor code Q C-CODE ; wherein the second cutoff frequency f 1 =(N×f 0 )+Δf, where Of is a cutoff frequency offset for the second desired bandwidth BW 1 .
14. The device of claim 13 , wherein the calibration circuitry is further configured to calibrate for mismatch between the first low-pass filter and the second low-pass filter by: determining a fractional capacitor code CI FRAC corresponding to the first desired bandwidth BW 0 , the fractional capacitor code CI FRAC being a value that lies between two consecutive capacitor codes [I CODE , I CODE+1 ], and that ideally corresponds to both a zero phase difference and a zero power difference between the first low-pass filter and the second low-pass filter; and using the fractional capacitor code CI FRAC to determine the capacitor code offset ΔI OFFSET and ΔQ OFFSET .
15. The device of claim 14 , wherein the calibration circuitry is further configured to determining the fractional capacitor code CI FRAC by: interpolating a line using a plurality of points with each point having a first dimension being a combined I-Q capacitor code [I CODE , Q CODE ], and a second dimension being a respective measured phase offset between the first low-pass filter and the second low-pass filter using a respective combined I-Q capacitor code; and selecting a combined I-Q capacitor code value that corresponds to a substantially zero phase difference between the first low-pass filter and the second low-pass filter.
16. The device of claim 15 , wherein the calibration circuitry is further configured to use the fractional capacitor code C FRAC to determine the capacitor code offset Δ OFFSET by: rounding the fractional capacitor code C FRAC to a nearest integer to produce the capacitor code offset Δ OFFSET ; adding the capacitor code offset Δ OFFSET to the first capacitor code I CODE to produce the first compensated capacitor code I C-CODE ; and adding the capacitor code offset Δ OFFSET to the second capacitor code Q CODE to produce the second compensated capacitor code Q C-CODE .
17. The device of claim 15 , wherein using the fractional capacitor code CI FRAC to determine the capacitor code offsets ΔI OFFSET and ΔQ OFFSET includes: rounding to the nearest integer [(1+αΔfc)*ΔC FRAC ] to produce the capacitor code offsets ΔI OFFSET and ΔQ OFFSET , where ΔC FRAC is a difference between the first capacitor code CI FRAC and the second capacitor code Q CODE , a is a scaling factor derived from empirical data, and Δfc is a capacitor code difference corresponding to the cutoff frequency offset Δf; adding the capacitor code offset ΔQ OFFSET to the first capacitor code I CODE to produce the first compensated capacitor code I C-CODE ; and adding the capacitor code offset ΔQ OFFSET to the second capacitor code Q CODE to produce the second compensated capacitor code Q C-CODE .
18. The device of claim 11 , wherein the device is configured to: applies the first compensated capacitor code I C-CODE to the first low-pass filter; and applies the second compensated capacitor code Q C-CODE to the second low-pass filter.
19. A wirelessly operating device that incorporates the device of claim 11 .
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
December 4, 2014
February 23, 2016
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