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Microwave
Digital Driver Unit with Linearization and Temperature Correction for Solid State Voltage Controlled Attenuators VCVA series

 

ELVA's Digital Driver Unit DVC-RS232 series intended for PC-based control on the Voltage-Controlled Variable Attenuators VCVA series through RS-232 serial port. The main feature of the driver is its built-in linearization capabilities of attenuation. The 12bit internal code allows DVC-RS232 logic chipset to linearise an attenuation curve with attenuation accuracy not worse than 0.1dB. Each driver is precisely calibrated with an each specific VCVA, and they both are shipped as whole unit.

As an option, temperature correction sensor available for Digital Driver Unit.

Main Features

  • 0-100dB, covered in 255 steps
  • 8bit input control code allows 255 steps of attenuation, one character per attenuation setting
  • <100 s switching time
  • Built-in capability of linearization of attenuation
  • Precisely calibrated for VCVA when shipped

DVC-RS232 Specs and Linearization Plot

The DVC-RS232 has the performance characteristics described in the following table. The DVC-RS232 driver includes linearization for the VCVA attenuator, permitting attenuation setting with +/- 0.1 dB accuracy in 255 steps within attenuation range.
 

Interface

Serial RS-232

Connector

DB-9 Male

Resolution

8 bits (character length on the serial interface, one character per attenuation setting)

Bit Rate

19200 bps fixed (max 115200)

Protocol

8N1 (8 data bits, no parity, one stop bit)

Flow control

None

MTBF

> 30,000 hours


Fig.1 DVC-RS232 linearization plot
(Blue line - before linearization, red line - with linearization)

Temperature Correction for Attenuator Digital Driver Unit

For temperature correction for Digital Driver Unit for Voltage-Controlled Variable Attenuator of VCVA series the AD7816 temperature sensor chip has been used . The AD7816 temperature sensor is a commercially available chip which allows obtaining an ambient temperature via serial interface. AD7816 was installed on VCVA chassis and connected to PROM memory (photo on fig.2). For transmitting AD7816 signals into the attenuator driver unit we replaced standard DB9 output connector to enhanced DB19 connector and made a special cable with an extender for RS-232 interface.

Digital Driver Unit of Voltage-Controlled Variable Attenuator
Fig.2. Photo of Digital Driver Unit with AD7816 temperature sensor chip

Calibration procedure was as the following:

1. We obtained nonlinear dependencies attenuation vs. input code and temperature. These dependencies are shown on Fig 3.

Diagram 1 for Digital Driver Unit of Voltage-Controlled Variable Attenuator
Fig.3. Dependencies of attenuation vs. input code and temperature

2. Achieved data was recalculated for obtaining a linear dependence attenuation vs. input code. Such wise we have 7 corrected dependencies for different temperature: +10C, +15C+40C (Fig.4).

Diagram 2 for Digital Driver Unit of Voltage-Controlled Variable Attenuator
Fig.4. Corrected curves for temperature range from +10C to +40C

3. We rewrote software inside the PROM, so it can read temperature from AD7816 chip and correct VCVA output code according to obtained temperature. Software uses linear approximation between 7 calibration tables for different temperatures. The final temperature test for VCVA Ser.Num.0076 is presented on Fig.5. These curves show the difference between an ideal linear attenuation (Code*0.125dB) and real attenuation level in dB.

Diagram 3  for Digital Driver Unit of Voltage-Controlled Variable Attenuator
Fig.5. Attenuation numbers with temperature correction for VCVA Ser.Num.0076

Digital Driver Unit for Solid State Voltage Controlled Attenuators of VCVA series can be shipped with temperature correction as an option.