Novatel Communications Ltd.

Russell E Braathen

Ronald P Green

An amplifier circuit for providing precise linear control over the output of a nonlinear amplifier, including a nonlinear gain controllable amplifier and an output control circuit. The output control circuit is connected to sample the signal output by the nonlinear amplifier. The amplifier output signal may be a continuous or a discontinuous signal. The output control circuit also receives a baseband signal. The sampled amplifier output signal and the baseband signal are alternatively transmitted to a detector. The detector produces a signal representative of the power level of either the sampled amplifier output signal or the baseband signal. The signals produced by the detector are stored separately in a pair of sample-and-hold circuits. A difference amplifier determines the difference between the stored signals and transmits this difference signal to the gain control input of the amplifier. The output signal from the amplifier is thereby adjusted to linearly track the baseband signal.

Linearized output control of a nonlinear amplifier

An active filtering mixer has a feedback arrangement, by means of which unwanted components in the output of the mixer are fed back, out of phase, to an input of the mixer for substantially canceling such components dynamically within the mixer, itself. In so doing, active filtering mixers in accordance with the invention largely avoid the undesirable effects these components can have on signal processing in downstream devices, and within the mixer. The feedback arrangement also stabilizes the mixer's DC operating point, and thereby can maintain the maximum dynamic range of the mixer. Preferably, the desired components of the output are also fed back, but to a substantially smaller degree than the unwanted components, thereby linearizing the in-band output of the mixer, and generallly improving the mixer's performance over the entire spectrum of its output.

Active filtering mixer

An electrical signal filter composed of a pair of cascaded filter sections in which the group delays of the two filter sections are matched so that their non-linear effects cancel in the passband, resulting in an overall linear phase. In addition, the attenuation slope after the first null in one filter section's stopband response is complemented by the other filter's stopband attenuation. This prevents the overall stopband attenuation from falling to extremely low values as with some filters, which, in turn, limits the time domain overshoot. The passband group delay and stopband attenuation characteristics are controlled by appropriate selection of the passband ripple and filter order number parameters of the filter. In a preferred embodiment, the two filter sections are of the elliptic and Chebyschev type. The invention can be implemented as analog-component active filter circuit or as a digital filter.

Linear phase low pass filter

A logarithmic periodic antenna is constructed with antenna elements implanted in a single plane in or on a surface of an insulating substrate. The substrate supports the co-planar antenna elements and keeps them in the desired configuration. The antenna elements are arranged in pairs, with the elements of a given pair being on alternate sides of a center conductor. The center conductor consists of two conducting strips, or feeders, which run down the middle of the antenna structure. Each of the feeders connects to a different one of a pair of elements, and each feeder connects to alternating elements of consecutive pairs, for example, to the 'left' element of one pair and the 'right' element of the next pair. The logarithmic periodic antennas may be used, without signal degradation, as both transmitting and receiving antennas in split-frequency communications systems. These antennas, which have minimal back and side lobe amplitudes, may be configured in an array by being mounted on a single mast and at the same height.

Logarithmic periodic antenna

An improved circuit for controlling the output power level of a radio frequency (RF) amplifier is disclosed. The circuit samples the output of an RF amplifier. The sample is amplitude modulated at a preselected modulation frequency and is passed to a detector. In repsonse to the amplitude modulated signal, the detector produces a signal whose amplitude is indicative of the RF amplifier's output power and whose frequency is the modulation frequency. The amplitude of the signal produced by the detector is then compared to a reference amplitude and the difference (error signal) is used to control the gain of the RF amplifier.

RF power-control circuit

An improved circuit for controlling the output power level of a radio frequency (RF) amplifier is disclosed. The circuit samples the output of an RF amplifier. The sample is amplitude modulated at a preselected modulation frequency and is passed to a detector. In response to the amplitude modulated signal, the detector produces a signal whose amplitude is indicative of the RF amplifier's output power and whose frequency is the modulation frequency. The amplitude of the signal produced by the detector is then compared to a reference amplitude and the difference (error signal) is used to control the gain of the RF amplifier.

A two way telephone communication system includes a station having a signal transmitting channel for conveying a signal received at a microphone to another station, a signal receiving channel for conveying signals received from the other station to a speaker, and switches permitting the two signal channels to be selectively enabled or disabled. Two signal detection paths are associated with the transmitting and receiving channels, each containing circuitry which detects the presence of signals in one of the channels and responds by generating actuating signals. Control circuitry responds to the detection path which first generates an actuating signal by enabling its associated signal channel and simultaneously disabling the other signal channel, triggering the switches appropriately. Delay circuitry associated with each signal detection path can be selectively enabled to delay the generation of an actuating signal in the associated signal detection path. The delay circuitry of the signal detection path associated with the disabled signal channel is enabled so long as signals are present in the enabled signal channel. This arrangement tends to maintain the enabled signal channel until it is no longer required to convey signals.

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Calgary, Canada

Russell E Braathen