A PE43711 Step Attenuator

1 Features

Insertion loss: 1.5dB for 9kHz to 1GHz, 2.0dB for 1 to 2GHz, 2.5dB for 2 to 4GHz.
Error at 30dB attenuation of \(\pm 0.5\) dB from 9kHz to 2.5GHz and \(\pm 1.0\) dB from 9kHz to 4GHz. Usable to 6GHz with increased attenuation error.
Input 0.1dB compression: 31 dBm.
Input IP3: 56 dBm.
Choice of SMA or MMCX connectors.

2 Typical Performance Characteristics

2.1 Insertion Loss

For the insertion loss, a linear fit gives good results as shown in Figure 1. For insertion loss:

\begin{equation*} \textrm{Loss (dB)} = A - Bf \end{equation*}

with: \(A = -1.17\), \(B = -3.29\times 10^{-4}\) and \(f\) is the frequency in MHz.

SMA board loss — **Figure 1**: Step attenuator SMA board insertion loss as a function of frequency. The dashed red line shows the associated linear fit.

2.2 Attenuation

SMA attenuation — **Figure 2a**: Step attenuator SMA board attenuation relative to insertion loss.

MMCX attenuation — **Figure 2b**: Step attenuator MMCX board attenuation relative to insertion loss.

2.3 Attenuation Accuracy

SMA accuracy — **Figure 3a**: Step attenuator SMA board attenuation accuracy.

MMCX accuracy — **Figure 3b**: Step attenuator MMCX board attenuation accuracy.

2.4 Input Return Loss

SMA S11 — **Figure 4a**: Input return loss for the step attenuator SMA board.

MMCX S11 — **Figure 4b**: Input return loss for the step attenuator MMCX board.

2.5 Isolation

SMA isolation — **Figure 5a**: Step attenuator SMA board isolation relative to reverse insertion loss.

MMCX isolation — **Figure 5b**: Step attenuator MMCX board isolation relative to reverese insertion loss.

2.6 Output Return Loss

SMA S22 — **Figure 6a**: Output return loss for the step attenuator SMA board.

MMCX S22 — **Figure 6b**: Output return loss for the step attenuator MMCX board.

The serial peripheral interface (SPI) is used to set the board attenuation level. Figure 7 illustrates the SPI setup of an attenuator board with the atmega USB controller which is running the ECApp embedded control firmware. In this configuration, the atmega board becomes the SPI master with the attenuator board being the slave. When connected to a host computer, the USB port of the atmega board also powers the attenuator board.

The rfblocks Python package provides the PE43711Controller and pe43711 classes which can be used for software control of the attenuator board. The code snippet below shows a minimal example of how the attenuator board is initialized and an attenuation level set. In this example the attenuation level is set to 16dB.

>>> import serial
>>> from rfblocks import pe43711, PE43711Controller, create_serial

>>> ser_device = '/dev/tty.usbmodem14101'
>>> ser = create_serial(ser_device)
>>> att = pe43711('D0')
>>> ctl = PE43711Controller('att1', att)
>>> ctl.initialize(ser)
>>> ctl.attenuation = 16.0
>>> ctl.configure(ser)

The code does the following:

Import the rfblocks pe43711 class and some support functions.
Open the USB/RS-232 serial device which connects the host computer to the ECApp control firmware running on the atmega microcontroller board.
Create an instance, att, of the pe43711 class. The attenuator board's latch enable (LE) pin is connected to the atmega controller PD0 pin and this is specified when creating att.
Create an instance, ctl, of the PE43711Controller class.
Initialize the attenuator contoller. This sets the required atmega controller pin states.
Set the controller attenuation level.
Configure the attenuator hardware with the attenuation level.

3.1 Board connector configuration

**Table 1**. Board pin configuration and function descriptions
Board Pin	Type	Description
`LE`	Input	Serial interface enable
`SI/C8`	Input	Serial interface data input. (For modules configured
		for parallel operation this is the parallel control
		bit, 8 dB.)
`Clk/C16`	Input	Serial interface clock input. (For modules configured
		for parallel operation this is the parallel control
		bit, 16 dB.)
`C4`	Input	Parallel control bit, 4 dB
`C2`	Input	Parallel control bit, 2 dB
`C1`	Input	Parallel control bit, 1 dB
`C0.5`	Input	Parallel control bit, 0.5 dB
`C0.25`	Input	Parallel control bit, 0.25 dB
`5V`	Power Input	5V DC power input
`Gnd`	Power Input	Module ground
`RF In`	Signal Input	Female SMA or MMCX connector for RF1 attenuator port (input)
`RF Out`	Signal Output	Female SMA or MMCX connector for RF2 attenuator port (output)

SMA conn. layout — **Figure 8a**: Step attenuator module connector layout (SMA connectors)

MMCX conn. layout — **Figure 8b**: Step attenuator module connector layout (MMCX connectors)

4 Reference designs

5 Design Notes

The control interface for the board may be either parallel or serial (SPI) depending on how on board components are populated. The schematic illustrated in Figure 9 shows the component placements for using SPI control.

Optional filtering is provided on both power and SPI control lines. This is to control possible low level spurious signals which can compromise the quality of the signal when cascading multiple step attenuator boards to implement high attenuation levels. For general use, a single 22pF shunt capacitor is sufficient for the SPI control lines with \(0\Omega\) jumers replacing the inductors L1, L2 and L3.