Cocoon Workshop, November, 8th 2012
Group Delay Impact in Tunable Impedance Matching
Networks Based on Ferroelectric Varactors
Erick González-Rodríguez, Holger Maune, Yuliang Zheng, Mohsen Sazegar, Rolf Jakoby
1. Efficiency in Receiver Architectures
• Radio communication systems  Maximum bandwidth efficiency at a given
modulation scheme and lowest power consumption:
• Optimized RF components.
• Matching networks.
• Filters.
2. Tunable Matching Networks
• Different environmental scenarios
 change of the input impedance.
• Matching networks with tunable
components  fixes the emerging
mismatch of the antenna at the
terminal side.
• Quality of signal degrades during its propagation towards the receiver.
• Analysis of RF components with the strongest influence.
• Enhancement of the same
communication system by using agile
components.
* CST, Computer Simulation
Technology AG.
Barium-Strontium-Titanate (BST) Ferroelectric Varactors
• Permittivity of this material can be tuned by an external continuous DC
voltage  tunable capacitance.
Fig. 1:
Receiver chain with different RF components.
 Low-power consumption
 Fast tuning
 High linearity
3. S-parameter Measurement and
Group Delay Analysis
• S-parameter measurements of TMN module tuned from 0 to 90 V (0.31 to
0.22 pF).
• Characteristics of modulated RF signal for analysis:
• Selected carrier frequency fc = 1.9 GHz.
• Signal bandwidth BW3dB = 20 MHz.
Fig. 2: Left: Equivalent circuit of matching network in T configuration. Right:
Tunable matching network in the center of a test board.
4. Bit Error Rate Results of
Matching Network
• Influence of overall group delay variation across the signal bandwidth
 up to 1dB in SNR when the tunability varies from 0% to 100%.
Fig. 3: Left: Forward reflection magnitude of the TMN module. Right: Forward
transmission magnitude of the TMN module.
• Difference in the phase of s21 and group delay for different tuning voltages.
Fig. 5: Left: Raw BER comparison of different ZL tunable states. Right: Exploded
view of raw BER.
Fig. 4: Left: Forward transmission phase. Right: Forward transmission group
delay.
Future Work
• Nonlinear analysis of multiband components.
• Integration of tunable components, e.g. TMN in a Software-Defined-Radio or
Cognitive Radio platform.
Related Work
[1] E. González-Rodríguez et al. “Impact of Group Delay on Tunable
Impedance Matching Networks Based on Barium-Strontium-Titanate
Varactors,” IEEE ISSSE 2012.
[2] K. Hofmann et al. “Fully Integrated High Voltage Charge Pump for Energyefficient Reconfigurable Multi-band RF-Transceivers,” IEEE INTELEC 2012.
Cooperation / Network
This work was supported by the LOEWE Priority
Program Cocoon (www.cocoon.tu-darmstadt.de).