N1045A/B Electrical Remote Sampling Head Module

The N1045A/B electrical sampling head modules provides 2 or 4 measurement channels with either 1.85 male or female RF input connectors. The module occupies only one of the four module slots on the 86100D. Because the N1045A/B remote heads contain the sampling electronics, the distance between the sampling and the probe stations or the device under test (DUT) can be made with very short or without cabling. By using a reduced amount of cabling, measurement degradation is minimized. The result is more accurate high-speed electrical measurements. This module scales the input signal, sets the bandwidth of the system, and allows the offset to be adjusted so the signal can be viewed. The output of the module is an analog signal that is applied to the ADCs on the acquisition boards inside the mainframe.

When four N1092D DCA-M optical sampling oscilloscopes are connected to an 86100D that has four N1045A/B-04X mini-modules, you have a total of 16 optical channels and 16 electrical channels. All of the 32 channels can be displayed at the same time.

Option IRC

Option IRC provides optical channel System Impulse Response Correction (SIRC) measurement and data files. These files provide an ideal channel response. SIRC data can be applied in the System Impulse Response Correction dialog. The SIRC correction data feature is a digital filter that is used to:

• Improve the response of module reference filters to more closely match an ideal receiver.
• Enable non-standard reference receiver rates or bandwidths.
• Increase the bandwidth of the channel by up to 50%.
• Ensures that an eye diagram will look identical between different modules.

SIRC correction data is unique to a specific module (serial number). Option IRC ships standard with every module and does not need to be purchased.

See Also

• Fixture Deskew
• Available Accessories
• Modules

To make a direct RF connection to a remote sampling head connector

The N1045A/B comes with either two 1.85 mm remote sampling heads (options 02M or 02F) or four 1.85 mm remote heads (options 04M or 04F). Option 02M and 04M connections are male center contacts and female outside threads. Option 02F and 04F connections are female center contacts and male outside threads.

1. Work at a static-safe workstation.
2. Visually inspect the connectors. If necessary, clean the connectors. Carefully align the connectors. The male connector center pin must slip concentrically into the contact fingers of the female connector.
3. Push the connectors straight together.

Do not twist one connector into the other (like inserting a light bulb). This happens if you turn the device body rather than the connector nut. Major damage to the center conductor can occur if the device body is twisted.

Do not tighten this connection. At this point all you want is a connection in which the outer conductors make gentle contact at all points on both mating surfaces. Very light finger pressure (no more than 2 inch-pounds of torque) is enough.


4. Using a torque wrench, make the final connection between the connectors while observing the following cautions. Using the torque wrench guarantees that a connection is not too tight, thus preventing possible connector damage. It also guarantees that all connections are consistently tight each time a connection is made.

To make a indirect RF connection to a remote sampling head connector

1. Work at a static-safe workstation.
2. Visually inspect the connectors. If necessary, clean the connectors. Carefully align the connectors. The male connector center pin must slip concentrically into the contact fingers of the female connector.
3. Push the connectors straight together.

Do not twist one connector into the other (like inserting a light bulb). This happens if you turn the device body rather than the connector nut. Major damage to the center conductor can occur if the device body is twisted.

Do not tighten this connection. At this point all you want is a connection in which the outer conductors make gentle contact at all points on both mating surfaces. Very light finger pressure (no more than 2 inch-pounds of torque) is enough.

Relieve any side pressure on the connection from long or heavy devices or cables. This will assure consistent torque when making the final connection.

4. Use an open-end wrench and a torque wrench to make the final connection between the connectors while observing the following cautions. The open-end wrench prevents any torque from being applied to the module's remote head connector. The torque wrench guarantees that a connection is not too tight, thus preventing possible connector damage. It also guarantees that all connections are consistently tight each time a connection is made.

To Deskew the Remote Sampling Heads

The following deskews are available:

• Skew calibration in the Calibration dialog box which removes any difference in the electrical lengths between the two remote sampling head cables.
• Auto Deskew located in the Differential Advanced Setup dialog which quickly deskews a differential signal for skew introduced by fixtures, the device-under-test and the source.
• Hardware Skew in the Advanced Setup dialog box which manually enters horizontal skew for an individual channel.

Changing the N1045A/B's bandwidth after performing any of the above three deskews degrades the applied deskew. If you need to change the module's BW while observing the DUT, use an Instrument Setup:

1. Connect the remote heads to the DUT.
2. For each BW setting:
1. Select the module's BW setting.
2. Perform the Auto Deskew.
3. Save the Instrument Setup. (File > Save > Instrument Setup)
3. Recall the Instrument Setup for the desired measurement BW. (File > Open Instrument Setup)

Keeping Your Test Setup Organized

If you install four N1045A/B modules, each with four remote heads, you'll have a total of 16 channel-input cables in your test setup. To help you manage all these cables and inputs, the module comes with a channel identification head LED, cable management clips, and head clips. The color of the head LED matches the color of the associated channel waveform.

Twenty-four cable clips, six each of yellow, red, blue, and green, are provided to keep differential cables together thus reducing cable tangling. The clip's color can also be used to associate a single head or differential pair of heads with a module slot.

Head brackets snap over two heads to connect them together. This is especially useful when making differential measurements.

Calibration

Unlike other modules, always attach a connector saver or cable to the input connectors before calibrating an N1045A/B. Do not provide any signal. Because each remote head's sampler is located near the input connector, this technique improves calibration accuracy by increasing thermal stability and by eliminating sampler reflections as explained in the following text. The mass of the cable or connector saver affects the sampler thermal equalibrium of your test setup. Even small temperature changes during calibration can affect sampler bias levels which in turn affect bandwidth and amplitude accuracy. Every time a sampler fires, it sends a small amount of energy toward the remote head's input connector. This is normal and common in all instruments that employ a sampler directly connected to the input. Without a connector saver or cable connected, this energy reflects back so quickly that it affects the sampled calibration value. Any cable ≥1 inch (2.54 cm) long or even a connector saver, sufficiently extends the round trip time to eliminate this issue. It is not necessary to terminate the far end of the cable or connector saver.

In the module calibration dialog, a positive ΔT value indicates how many degrees warmer the current mainframe temperature is compared to the temperature of the mainframe at the time of the last module calibration. For N1045A/B modules, a positive ΔT value indicates how many degrees warmer the current remote head temperature is compared to the temperature of the remote head at the time of the last module calibration.

Monitoring a Head's Thermal Equilibrium

To monitor the thermal equilibrium of a remote head:

1. Click Tools > Calibrations on FLexDCA's menu to open the Calibrations dialog.
2. Click the N1045A/B tab.
3. Click the Details button for the remote head's channel. This views the following Vertical Calibration Details:
• Temperature change in °C for the remote head since the last calibration.
• "The temperature has changed by more than 5.00°C" is displayed if module needs to be calibrated.

Wait one minute then open the All Calibrations dialog again. If the temperature changes more than 0.5°C, the channel is not at thermal equilibrium.

Stabilizing the Temperature

Each remote head represents a relatively small thermal mass and meets specifications over a ±5°C range from the last calibration temperature, measured by the internal temperature sensor and reported in the All Calibrations dialog. Factors other than the ambient air temperature will affect the operating temperature of the remote head. These factors include air currents and the temperature and thermal mass of objects in contact with the remote head. You must ensure the temperature of the N1045A/B module is stabilized prior to calibrating the module and making measurements. As with all plug-in modules, the temperature is stabilized after 1 hour of continuous operation. The preferred method to stabilize the temperature of the N1045A/B is to set up the module and remote heads in the configuration or fixture that will be used to make measurements. This includes connecting the device under test (DUT) to the remote heads.

When the internal temperature is stabilized, disconnect the DUT and perform a module calibration. If you move the remote head to a location that is thermally different than the location in which it was stabilized, you will have to wait for the temperature to stabilize again, and then calibrate the module before making measurements. For example, if the remote head is placed on a workbench for an hour, and then mounted on a cool metal fixture to make measurements, the temperature of the sampling head will begin to drop, possibly out of the ±5°C range.

Recommendations

• Ensure that the remote head's entire surface is never outside a 15°C to 35°C temperature range.
• Verify temperatures using a thermometer. The hottest locations are likely close to the input connector and the center of the head's sides.
• If possible, leave an air gap between remote heads.
• Use forced airflow.
• When designing a cooling system, anticipate that each remote head can generate between 1 and 3 Watts of heat.
• Although the module's remote-head cable can sustain at least a 100 °C surface temperature, the cable's color might degrade if exposed to high temperatures for long periods of time. This does not damage the cable.

Secure the Remote Heads

To prevent the mass of the cable from pulling the remote head off a benchtop or out of a test fixture, five threaded mounting holes are provided as shown in the following picture. The five holes use M3 x 0.5 mm threads. Using these holes, you can attach the head to your own custom fixture. Or you can use an accessory universal bracket (N1027A-1PB) to attach the head to a probe positioner. It is important to consider the thermal properties of the remote head when designing a fixture. Larger fixtures increase the thermal mass of the remote head, which increases the time the remote head takes to reach thermal equilibrium.

Stability of the Remote Head Cables during Measurements

The remote head cable carries the high frequency content of the timebase signal. Changes to the physical shape of the cable (for example, bending or twisting) may horizontally skew the signal on the display screen. Changes in the shape of the cable cause variations in the effective electrical length of the cable, which translates directly to horizontal timing variations. This is important to be aware of when making jitter measurements. Vibration is similar to cable movement. Vibrating the cable may also horizontally skew the signal on the display screen. Temperature changes can also result in timing variations by adding femto or even pico seconds of change in electrical length. This electrical length change is due to the thermal expansion and contraction of the remote head cable. Use tape, cable ties, and the provided cable clips to stabilize the cables to minimize the affects of phase shift.

Supplied Accessories

Description	Quantity
Module configuration card.	1
1.85 mm protective cap for 02F and 02M options	2
1.85 mm protective cap for 04F and 04M options	4
Cable management clips. One each yellow, green, blue, red.	4
Head clip	2

Options

Option	Description
N1045-02M	2 Channel Remote Head with 1.85 mm (m) connectors.
N1045-02F	2 Channel Remote Head with 1.85 mm (f) connectors.
N1045-04M	4 Channel Remote Head with 1.85 mm (m) connectors.
N1045-04F	4 Channel Remote Head with 1.85 mm (f) connectors.

Available Accessories Specific to the N1045A/B Module

Description	Item
Replacement cable management clips. Quantity 24, six each yellow, green, blue, and red.	N1027A-1CL
Replacement head clip. Quantity 1.	N1027A-2CL
Universal probe-head-to-probe-positioner bracket. The bracket is designed to fit over 1/4-inch diameter dowel on probe positioner.	N1027A-1PB
Protective cap for 1.85 mm female connector	N1027A-1CF
Protective cap, 1.85 mm male connector	N1027A-1CM
Adapter, 1.85 mm (f-f)	N1027A-1FF
Adapter, 1.85 mm (m-f)	N1027A-1MF
Adapter, 1.85 mm (m-m)	N1027A-1MM
Adapter, 2.4 mm (m) to 3.5 mm (m)	N1027A-23A
Adapter, 2.4 mm (f) to 3.5 mm (f)	N1027A-23B
Adapter, 2.4 mm (m) to 3.5 mm (f)	N1027A-23C
Adapter, 2.4 mm (f) to 3.5 mm (m)	N1027A-23D
2.4 mm DC block, 16V, 50 kHz to 50 GHz	N1027A-2DC
Accessory case	N1027A-1AC
Module storage case	N1027A-1MC