Integrated bidirectional junction engineered dual insulator transceiver

A bi-directional transceiver (100) having reduced circuitry and that may be formed on a non-semiconductor substrate includes impedance matching and filtering circuitry (114, 116, 122, 124, 128, 132) coupled to a non-linear diode (118) for converting a lower frequency modulated signal to a higher frequency RF transmit signal and to function as a square-law detector to envelope detect RF signals. The non-linear diode (118) includes, in one exemplary embodiment, at least two insulative layers disposed between two conductive layers, wherein a quantum well is formed between the insulators that allows only high-energy tunneling.

FIELD

The present invention generally relates to bidirectional communications and more particularly to transceivers used in bidirectional communications.

BACKGROUND

Typically, complex RF front ends have separate transmit and receive functions, which is accomplished by the use of separate antennas, separate transmit and receive frequencies, and a transmit/receive switch. Conventional transceivers typically have four amplifiers, an RF amplifier and an intermediate frequency amplifier in each of a transmit section and a receive section. Furthermore, typical front ends require assembling integrated circuit chips onto a packaging platform, involving expensive semiconductor based technologies, and assembly in flip chip form, for example, to another substrate resulting in interconnect repeatability and yield issues. Circuit complexity, silicon area, and cost are reduced by integrating the transmit section and the receive section in one circuit.

Simultaneous two-way transmission of information signals in the same frequency band is disclosed in U.S. Pat. No. 7,187,907, wherein a complex semiconductor based adaptive filtering and a cancellation technique allows for a simultaneous bidirectional communications link.

A bidirectional amplifier is disclosed in U.S. Pat. No. 5,821,813, wherein a coupler at the antenna separates signals to the mixer for demodulation and from a multiplier for transmission; however, a LO drive for the mixer is required.

However, known bidirectional transceivers require semiconductor technology. The active components in transmitters and receivers are based upon semiconductor technology, and typically require one integrated circuit or integrated circuit technology for the transmit section and another integrated circuit or integrated circuit technology for the receive section.

Accordingly, it is desirable to provide a bi-directional transceiver having reduced circuitry and that is capable of being formed on a non-semiconductor substrate. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.

DETAILED DESCRIPTION

Using a highly nonlinear diode such as a Schottky diode or the Junction Engineered Dual Insulator (JEDI) technology developed at the University of Colorado as described in U.S. Pat. No. 6,563,185, a single device can act both as an RF resistive multiplier to upconvert modulated signals to an antenna, and can also serve as a square-law detector or envelope detector to incoming RF signals. Through the use of JEDI technology, low cost, half-duplex, integrated RF front ends may be fabricated on these non-semiconductor substrates such as FR-4 boards or any material including, for example, quartz, ceramics, Teflon, polyimides, plastic, liquid crystal polymer, and epoxy. Improved performance is accomplished by eliminating or reducing lossy interconnects, and positioning the demodulator in the vicinity of the antenna.

The JEDI technology comprises nanoscale stacks of metals and insulators for creating ultra-high frequency diodes, antennas, and transistors operating at frequencies from DC to 3.0 THz. More specifically, a second layer of insulator and metal may be substituted for the semiconductor found in metal-oxide semiconductors, resulting in a four-layer stack of metal-insulator-insulator-metal (MIIM). A quantum well is formed between the insulators that allows only high-energy tunneling. Consequently, when a voltage is applied to the top metal that exceeds its threshold, a ballistic transport mechanism accelerates tunneling electrons across the insulator gap.

A single device is used in a bi-directional manner near a single antenna, using planar filters and is operated in a half-duplex mode to provide a simple RF front end that can be fully integrated on the RF board used for the antenna by the use of a thin film JEDI device providing the non-linear response to RF signals required for multiplication and detection.

Referring toFIG. 1, a bi-directional transceiver100includes a modulated transmit signal terminal102, a modulated transmit/receive terminal104, and a demodulated receive signal terminal106. An amplifier110has an input coupled to the modulated transmit signal terminal102, and an output coupled to an integrated planar substrate108by a capacitor112. An input signal having a frequency, for example in the range of 1.0 Ghz to 100.0 Ghz, but preferably of approximately 30 Ghz, may be applied to the modulated transmit signal terminal102. The integrated planar substrate108comprises a low frequency material, such as a printed circuit board of FR-4 material.

In the transmit mode, the signal from the capacitor112is filtered by a band pass filter114and is matched to the diode118by matching circuitry116. The diode118is chosen to have a nonlinear I/V characteristic which, when excited by signals of sufficient amplitude, will distort the waveform and generate harmonic frequencies. The nonlinear characteristic is resistive in nature. In other words, as an applied RF signal202(FIG. 2) swings across the I/V characteristic of the diode118, the effective resistance is changing in a time varying manner producing a nonlinear distortion in the time domain waveform. It is noted the anode and cathode of the diode118may be reversed in the circuit, but may require a different biasing scheme.FIG. 2shows a representative I/V characteristic with the applied RF signal producing an asymmetric swing due to the nonlinearity of the diode118. As the RF signal202applied to the diode118, the point on the I/V curve202will move back and forth along the curve202from the quiescent operating point204. This may be seen by the graphical representation of the asymmetric current movement206and the asymmetric voltage movement208.

FIG. 3shows an exemplary time domain waveform302before distortion, andFIG. 4shows an exemplary time domain waveform402after distortion introduced by the diode118nonlinearity. This type of distortion produces frequency domain components at harmonics of the applied RF frequency. By designing the matching116,122and filter114,124circuits to optimize the desired harmonic frequency (usually the 2ndharmonic), a frequency multiplier is produced. An example of the multiple harmonic signal402from the diode is represented by the graph inFIG. 5. The input signal302,502and higher harmonic signals504are minimized, while the second harmonic signal506is maximized. Note the second harmonic signal506is at 60 GHz, twice the frequency of the input signal502.FIG. 6shows a representative frequency domain spectral output. The output signal from the diode118is impedance matched to the filter and antenna at the desired frequency by a matching circuit122and undesired frequencies are filtered by the band pass filter124centered at the desired output frequency. A DC ground return path or bias voltage126, may be applied through a low pass filter/RF choke circuit128. Some diode devices may perform better or provide some tunability through use of an applied bias.

The transmit signal is preferably coupled to an on-board planar antenna104(FIG. 1) integrated onto the substrate108, although an off-board antenna (not shown) may be used. Without further transmit amplification, this type of transmit topology is most useful where low transmit powers are acceptable such as for short range point to point communications. While the substrate may be a semiconductor material, it preferably is a non-semiconductor material, for example, including at least a portion selected from one of the group consisting of quartz, ceramics, Teflon®, polyimides, plastic, liquid crystal polymer, and epoxy.

In the receive mode, an amplitude modulated signal can be demodulated by using the diode118as square law or envelope detector.FIG. 6illustrates an example of this type of detection. The signal602received at terminal104is filtered through the same pass band filter124used in transmission. The signal to the diode118is optimized by the same matching circuit122used in transmit mode. The impedance matching between the diode118and the filter124optimizes both the transmit and receive functions. The impedance matching between the diode118and the lower frequency filter114on the transmit side optimizes the transmit function and does not impact the receive function. The same nonlinear diode118characteristics which enable frequency multiplication enable direct detection of amplitude modulated carrier frequencies. The incident RF signal is converted to a DC signal proportional in amplitude to the power absorbed from the RF signal.FIG. 7illustrates a typical diode detector responsivity curve702. The low pass filter/RF choke132removes the carrier frequency and passes the modulated baseband signal to the load resistor136. The DC voltage generated by the detector can be increased by increasing the impedance load on the diode, but at the expense of the video bandwidth, which is related to the time constant of the load impedance in series with the diode capacitance. If the impedance looking into the baseband amplifier134is high, the impedance is set primarily by the load resistor136. The signal is then applied to the baseband amplifier134which amplifiers the detected signal for processing by the baseband circuitry (not shown).