Ring filter synthesis and its BiCMOS 60 GHz implementation

Abstract

The detailed synthesis of a direct access ring filter topology fully controlled with the following targeted specification (center frequency, low transmission zero frequency, and matching level in the passband) is hereby presented. For this topology, the lowest achievable bandwidth is limited by technological constraints. Thereby a solution consisting in adding capacitive loads is proposed. The associated synthesis is also given and discussed. Both syntheses are illustrated with 60 GHz integrated planar filters implemented in the IHP 130 nm BiCMOS technology. Various 3 dB fractional bandwidths from 18 to 8% are targeted, some of them require the implementation of the capacitive loaded solution. The latter allows us to lower the bandwidth limit of the nominal topology as well as to get a high miniaturization, up to 3.4, depending on the capacitance value. Thanks to good measurement results, this implementation highlights the high efficiency, reliability, and versatility of the synthesis without the need of tuning simulations or post-simulations.

Synthesis of a tunable ring filter: Proof‐of‐concept with fixed implementations at D‐band

“…The design procedure is the following. Considering that the high frequency state is realized fixing Z c1 and the matching level equal to 50 Ω and 60 dB, respectively, the designer chooses the center frequency f high , low-transmission zero f z and 20 imposes the miniaturization capacitance C m , it gives us the impedance Z c2 and the electrical lengths θ c1 , θ c2 .…”

“…Nevertheless, the return loss being explicitly set by the impedance values, 20 the low frequency matching cannot be controlled this way. Keeping the symmetry, it has been observed that a reasonable capacitor imbalance while maintaining a constant value for the sum of the capacitances allows to keep the same low frequency.…”

“…The current paper introduces a tunable filter synthesis relying on capacitors displacement along a ring resonator (see 20 for the fixed frequency synthesis). The principle of a capacitor displacement has already been used in Reference 21 around 2 GHz: A varactor connected in series inside a resonator leads to reconfigurable bandpass filters with predefined tuning range depending on the position of the varactors.…”

Synthesis of a Tunable Impedance Inverter Based on Variable Position of Capacitive-Loads

“…For the sake of illustration of the interest of such an inverter synthesis, a ring-based bandpass filter is designed [5]. It is based on the use of two pairs of quarter wavelength transmission lines with different impedances Z 1 and Z 2 (Fig.…”

“…3). The synthesis of the unloaded nominal filter was given in [5]. The filter bandwidth is ruled by the impedance ratio between Z 1 and Z 2 .…”