# US 11,029,348 B2 · Measuring a load resistance coupled to a transmission line

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- Number: US 11,029,348 B2
- Document ID: US11029348B2
- Status: Granted
- Kind: B2
- Application number: 16/186,207
- Filed: 2018-11-09
- Published: 2020-05-14
- Granted: 2021-06-08
- Earliest claimed: 2018-11-09
- Assignees: Western Digital Technologies, Inc.
- Applicants: Western Digital Technologies, Inc.
- Inventors: Sergey G. Muchiyev; Yaw Shing Tang; Cliff C. Zhang
- Web page: https://patentgrep.com/patent/US11029348B2

## CPC

- G01R 27/16: Measuring impedance of element or network through which a current is passing from another source, e.g. cable, power line
- G11B 5/48: Disposition or mounting of heads {or head supports} relative to record carriers {(mounting of head within housing G11B5/105); arrangements of heads, e.g. for scanning the record carrier to increase the relative speed (driving of both record carriers and head G11B15/18; guiding record carriers G11B15/60; head selecting circuits G11B15/12)}
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)
- G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R)

## Abstract

Measurement circuitry is disclosed that is configured to be coupled to a load through a transmission line. A first AC signal having a frequency ω1 is applied to the transmission line and a first input impedance of the transmission line is measured. A second AC signal having a frequency ω2 is applied to the transmission line and a second input impedance of the transmission line is measured, wherein the frequency ω2 is different than the frequency ω1. A third AC signal having a frequency ω is applied to the transmission line and a third input impedance of the transmission line is measured, wherein the frequency ω is different than the frequency ω1 and different than the frequency ω2. A resistance of the load is measured based on the measured first input impedance, the measured second input impedance, and the measured third input impedance.

## Claims

### Claim 1

Measurement circuitry configured to be coupled to a load through a transmission line, wherein the measurement circuitry is configured to:
apply a first AC signal having a frequency ω1 to the transmission line and measure a first input impedance of the transmission line;
apply a second AC signal having a frequency ω2 to the transmission line and measure a second input impedance of the transmission line, wherein the frequency ω2 is different than the frequency ω1;
apply a third AC signal having a frequency ω to the transmission line and measure a third input impedance of the transmission line, wherein the frequency ω is different than the frequency ω1 and different than the frequency ω2; and
measure a resistance of the load based on the measured first input impedance, the measured second input impedance, and the measured third input impedance,
wherein the frequency ω of the third AC signal is a quarter-wave resonance frequency of the transmission line such that a wavelength of the third AC signal is substantially equal to:
4
⁢
L
1
+
2
⁢
n
where:
L represents a length of the transmission line; and
n is an integer.

### Claim 2 (depends on 1)

The measurement circuitry as recited in claim 1, wherein n is zero such that a frequency of the third AC signal is a quarter-wave frequency.

### Claim 3 (depends on 2)

The measurement circuitry as recited in claim 2, wherein:
the frequency ω1 is half of the frequency ω; and
the frequency ω2 is 3/2 of the frequency ω.

### Claim 4 (depends on 3)

The measurement circuitry as recited in claim 3, wherein the measurement circuitry is further configured to calibrate the third frequency ω by:
while applying a calibration AC signal to the transmission line, adjusting a frequency of the calibration AC signal;
measuring a calibration input impedance of the transmission line at a plurality of the frequencies of the calibration AC signal; and
selecting the third frequency ω based on at least one of:
when a magnitude the calibration input impedance is near a maximum; or
when a phase of the calibration input impedance is near zero.

### Claim 5 (depends on 2)

The measurement circuitry as recited in claim 2, wherein:
the frequency ω1 of the first AC signal corresponds to an attenuation factor S(ω1) of the transmission line having a substantially zero real value; and
the frequency ω2 of the second AC signal corresponds to an attenuation factor S(ω2) of the transmission line having a substantially zero real value.

### Claim 6 (depends on 5)

The measurement circuitry as recited in claim 5, wherein the measurement circuitry is further configured to:
measure a first value ΓS(ω1) of the transmission line at the frequency ω1 based on a first phase of the first input impedance, and measure a second value ΓS(ω2) for the transmission line at the frequency ω2 based on a second phase of the second input impedance, where Γ represents a reflection factor of the transmission line;
measure an attenuation factor S(ω) of the transmission line at the frequency ω based on a ratio of the measured first value ΓS(ω1) and the measured second value ΓS(ω2); and
measure the resistance of the load based on the measured attenuation factor S(ω).

### Claim 7 (depends on 6)

The measurement circuitry as recited in claim 6, wherein the measurement circuitry is further configured to:
generate a characteristic impedance of the transmission line at the frequency ω based on the first measured input impedance and the second measured input impedance; and
measure the resistance of the load based on:
the measured attenuation factor S(ω) of the transmission line at the frequency ω;
the generated characteristic impedance of the transmission line at the frequency ω; and
the measured third input impedance of the transmission line at the frequency ω.

### Claim 8 (depends on 7)

The measurement circuitry as recited in claim 7, wherein the measurement circuitry is further configured to measure the resistance of the load based on:
Z
⁢
⁢
0
⁢
(
ω
)
=
[
Z
⁢
⁢
0
⁢
(
ω
)
⁢
(
S
⁡
(
ω
)
+
1
)
+
Zin
⁡
(
ω
)
⁢
(
S
⁡
(
ω
)
-
1
)
Zin
⁡
(
S
⁡
(
ω
)
+
1
)
+
Z
⁢
⁢
0
⁢
(
ω
)
⁢
(
S
⁡
(
ω
)
-
1
)
]
where Z0(ω) represents the characteristic impedance of the transmission line at the frequency ω, and Zin(ω) represents the measured third input impedance of the transmission line at the frequency ω.

### Claim 9 (depends on 1)

The measurement circuitry as recited in claim 1, further comprising a resistor bridge configured to couple to the transmission line.

### Claim 10 (depends on 1)

The measurement circuitry as recited in claim 1, further comprising a RF-IV circuit configured to couple to the transmission line.

### Claim 11 (depends on 1)

The measurement circuitry as recited in claim 1, wherein the load comprises a component of a head in a data storage device.

### Claim 12

A method of measuring a resistance of a load coupled through a transmission line to measurement circuitry, the method comprising:
applying a first AC signal having a frequency ω1 to the transmission line and measuring a first input impedance of the transmission line;
applying a second AC signal having a frequency ω2 to the transmission line and measuring a second input impedance of the transmission line, wherein the frequency ω2 is different than the frequency ω1;
applying a third AC signal having a frequency ω to the transmission line and measuring a third input impedance of the transmission line, wherein the frequency ω is different than the frequency ω1 and different than the frequency ω2;
processing the first input impedance and the second input impedance to measure a ratio:
S
⁡
(
ω
)
=
[
S
⁡
(
ω
⁢
⁢
1
)
S
⁡
(
ω
⁢
⁢
2
)
]
p
⁢
⁢
where
⁢
⁢
p
=
√
(
2
+
4
⁢
n
)
(
1
+
4
⁢
n
-
3
+
4
⁢
n
)
S(ω1) represents an attenuation factor of the transmission line at the frequency ω1, S(ω2) represents an attenuation factor of the transmission line at the frequency ω2, S(ω) represents an attenuation factor of the transmission line at the frequency ω, and n is an integer; and
measuring a resistance of the load based on and the measured third input impedance and the attenuation factor S(ω).

### Claim 13 (depends on 12)

The method as recited in claim 12, wherein the frequency ω of the third AC signal is a quarter-wave resonance frequency of the transmission line such that a wavelength of the third AC signal is substantially equal to:
4
⁢
L
1
+
2
⁢
n
where:
L represents a length of the transmission line; and
n is an integer.

### Claim 14 (depends on 13)

The method as recited in claim 13, wherein n is zero such that a frequency of the third AC signal is a quarter-wave frequency.

### Claim 15 (depends on 14)

The method as recited in claim 14, wherein:
the frequency ω1 of the first AC signal corresponds to the attenuation factor S(ω1) of the transmission line having a substantially zero real value; and
the frequency ω2 of the second AC signal corresponds to the attenuation factor S(ω2) of the transmission line having a substantially zero real value.

### Claim 16 (depends on 15)

The method as recited in claim 15, further comprising:
generating a characteristic impedance of the transmission line at the frequency ω based on the first measured input impedance and the second measured input impedance; and
measuring the resistance of the load based on:
the measured attenuation factor S(ω) of the transmission line at the frequency ω;
the generated characteristic impedance of the transmission line at the frequency ω; and
the measured third input impedance of the transmission line at the frequency ω.

### Claim 17 (depends on 16)

The method as recited in claim 16, further comprising measuring the resistance of the load based on:
Z
⁢
⁢
0
⁢
(
ω
)
=
[
Z
⁢
⁢
0
⁢
(
ω
)
⁢
(
S
⁡
(
ω
)
+
1
)
+
Zin
⁡
(
ω
)
⁢
(
S
⁡
(
ω
)
-
1
)
Zin
⁡
(
S
⁡
(
ω
)
+
1
)
+
Z
⁢
⁢
0
⁢
(
ω
)
⁢
(
S
⁡
(
ω
)
-
1
)
]
where Z0(ω) represents the characteristic impedance of the transmission line at the frequency ω, and Zin(ω) represents the measured third input impedance of the transmission line at the frequency ω.

### Claim 18 (depends on 14)

The method as recited in claim 14, wherein:
the frequency ω1 is half of the frequency ω; and
the frequency ω2 is 3/2 of the frequency ω.

### Claim 19 (depends on 18)

The method as recited in claim 18, further comprising calibrating the third frequency ω by:
while applying a calibration AC signal to the transmission line, adjusting a frequency of the calibration AC signal;
measuring a calibration input impedance of the transmission line at a plurality of the frequencies of the calibration AC signal; and
selecting the third frequency ω based on at least one of:
when a magnitude the calibration input impedance is near a maximum; or
when a phase of the calibration input impedance is near zero.