Automatic tuning of quality factors for VHF CMOS filters

A VHF transconductance-C filter technique with automatic tuning of the quality factors and the cutoff frequency, based on a voltage controlled oscillator (VCO), is presented. The Q-tuning circuit is very simple and contains no signal carrying nodes, resulting in a well-controlled Q up to very high frequencies (100 MHz). A breadboard realization of the Q-tuning circuit gave good result

Transconductor and integrator circuits for integrated bipolar video frequency filters

A description is presented of novel transconductor and integrator circuits which can be used in integrated video frequency filters in bipolar technology. The transconductor consists of a parallel connection of a passive nominal transconductance and an active variable transconductance, resulting in good high-frequency performance up to 70 MHz and less than 1% linearity error for input signals up to 2V pp. The integrator incorporates an operation transconductance amplifier circuit which provides a tunable integrator phase. Simulation results for all circuits and for a fifth-order elliptic low-pass filter with a nominal cutoff frequency of 5 MHz are presente

Accurate automatic tuning circuit for bipolar integrated filters

An accurate automatic tuning circuit for tuning the cutoff frequency and Q-factor of high-frequency bipolar filters is presented. The circuit is based on a voltage controlled quadrature oscillator (VCO). The frequency and the RMS (root mean square) amplitude of the oscillator output signal are locked to the frequency and the RMS amplitude of a reference signal, respectively. Special attention is paid to the actual Q-factor in the oscillator. Experimental results for a breadboard circuit operating from 136 to 317 kHz are presente

Two-lead multiplex system for sensor array applications

We present a multiplex system that creates the opportunity to use only two wires in sensor array applications, with arbitrary inter-sensor distances. The utility of this principle is shown by the realization of a CMOS prototype of this multiplexer

A CMOS OTA for HF filters with programmable transfer function

A CMOS operational transconductance amplifier (OTA) for programmable HF filters is presented. When used in an OTA-C integrator, the unity-gain frequency phase error remains less than 0.3° for frequencies up to more than one tenth of the OTA bandwidth. The OTA has built-in phase compensation, which allows tuning of the transconductance of the OTA (Gm) while maintaining a small phase error. Since this phase error is preserved over the Gm range of the OTA, the OTA is suitable for filters with a programmable transfer function. Using stacked square-law transistors improves the linearity, DC-gain, and power-consumption properties of the OT

Accurate automatic tuning circuit for bipolar integrated filters

An accurate automatic tuning circuit for tuning the cutoff frequency and Q-factor of high-frequency bipolar filters is presented. The circuit is based on a voltage controlled quadrature oscillator (VCO). The frequency and the RMS (root mean square) amplitude of the oscillator output signal are locked to the frequency and the RMS amplitude of a reference signal, respectively. Special attention is paid to the actual Q-factor in the oscillator. Experimental results for a breadboard circuit operating from 136 to 317 kHz are presente