Analog Hotspot

This circuit is a first-come, first-serve selector (see the figure). Its genesis comes from a teacher who asked me to create a "Jeopardy" style quiz show apparatus that offers a fun way to test students. Three contestants each have a simple single-pole, single-throw switch to activate when they know the answer. The first one who thinks he or she has the answer locks his or her light on and wins! The contestant switches are...

This article describes a design for a precision clock-generator circuit board that can function as a waveform generator in some telecom- or datacom-specific lab bench work. The clock generator outputs an array of clocks at fixed frequencies, and it accepts an external synchronization clock reference as an input. At the core of the design is U1, a ZL30407 Sonet/SDH network element phase-locked loop (PLL) (Fig. 1). The...

Multichannel television sound (MTS), better known as Broadcast Television System Committee (BTSC) encoding, is used in many analog cable set-top boxes for TV. The BTSC pilot is at the same frequency (15.734 kHz) as the horizontal video sync. The pilot signal is used to recover the L−R, SAP, and PRO audio channels. And by applying the principles of phase-locked loops (PLLs) and closed-loop feedback in a novel manner, it can generate the stable, high-speed master clock required to...

Interactive gaming consoles, digital TVs, and digital video recorders (DVRs), among other multimedia systems, benefit from higher levels of silicon integration. They achieve greater functionality, lower cost, better performance, and lower power consumption. In the many cases that call for very high-performance signal processing, silicon integration becomes a critical enabler. All of these multimedia systems have "front ends" containing analog/mixed-signal subsystems for...

Figure 1 shows a benign means of interfacing a low-level, wideband differential signal to an analog-to-digital converter (ADC). The FET input stage (AD8066) draws only 6 pA of input bias current and presents only 2 pF of differential input capacitance. The overall circuit has an input referred noise of 10 nV/√Hz and a gain-bandwidth product (GBP) of 2 GHz. It maintains a common-mode rejection ratio (CMRR) of over 90 dB up to 1 MHz, far...

The video circuit illustrated in Figure 1 combines an audio-subcarrier notch filter and group-delay equalization as required by the ITU-470 standard. It also includes an amplitude-adjustment capability for driving an RF video modulator in NTSC applications. (PAL operation requires a minor adjustment of the filter and all-pass values.) For best performance, the input should be driven from a low-impedance source, such as an op...

Some applications, such as audio equalizers, require bandpass filters with a constant maximum gain, independent of the selected quality factor Q. But in a lot of well-known filter structures—such as Sallen-Key, MFB, state variable, and Tow-Thomas—when you adjust the quality factor of the second-order cells, the maximum gain changes...

This simple serial RS-232-to-discrete-output application and driver, based on Texas Instruments' 74LV8153, requires only a minimum of parts. The single-wire, RS-232 bit-compatible 74LV8153 supports an internal clock, auto-baud function, and output registers. Graphic control written in Visual Basic (VB) gives this implementation a Windows-based feel. The circuit is intended as a resource for bench-switch or power-supply controls. Referring to the schematic in ...

Most LCD character displays connect to the outside world via a controller IC, such as the HD44780 (Hitachi) or equivalent. However, that interface has serious drawbacks. It uses a large number of the microcontroller's general-purpose I/O (GPIO) pins, and it can't provide digital contrast or backlight intensity control. The circuit in the figure reduces the required number of GPIOs from 11 to two while also supplying digital control of the LCD's contrast and backlight...

Small inductance changes on the order of 0.01% can easily be sensed over a wide range with a simple circuit connected to a serial port (see the figure). Using a classic Colpitts oscillator interfaced to an eight-pin Atmel ATtiny12-8 microprocessor, the period of multiple oscillator cycles—which is proportional to the inductance—can be sensed. Applications include metallic proximity sensing and seismic detection....

Switched-capacitor blocks are easily configured to be integrators. When configured as an integrator, a switch-capacitor block can function as an op amp. Closed-loop stability is achieved by parametrizing the capacitor values and sample frequency, which allow for precise gain-bandwidth control. Adding an external pass transistor and current-setting resistor enables easy construction of a programmable current source. Figure 1 shows...

The circuit that's shown in Figure 1 implements a programmable 0- to 20-mA precision current source. The REF192 low-headroom 2.5-V voltage reference (U1) can source up to 30 mA. An AD5280 digital potentiometer (U2) controls the voltage-divider ratio of the reference voltage. U3, an OP1177 op amp, closes the loop by forcing VL = VW. At the digital pot's zero scale, where VWB ≈ 0 V, the voltage across RSET will approach zero and...

A simple linear voltage-controlled amplifier can be constructed with one op amp and two JFETs (see the figure). The amplifier can achieve an 80-dB dynamic control range with less than ±0.2% linearity error for 0 V ¾ VC ¾ 0.8 × VP. JFETs act as linear resistors over a very small range of drain-to-source voltages (the ohmic region). In this circuit, an op amp constrains the...

Some of the many low-dropout (LDO) regulators supplying voltage regulation for electronic systems are designed for low noise. For example, the IC in Figure 1 achieves an RMS noise voltage of about 115 µV by itself. However, some ultra-low-noise applications such as instrumentation and high-quality audio require even lower noise. For that purpose, the Figure 1 circuit includes an external transistor and simple low-pass RC filter. Together, they reduce the supply noise by more...

According to FCC regulations, a telephone line in the on-hook state must not be dc loaded by less than 5 MV of resistance up to 100 V. Also, it must be galvanically isolated from the local ground. In the case of a standard dc line-feed of 48 V, this means that the dc load must be less then 10 µA. Furthermore, the tip and ring must be isolated by a transformer in case the telephone circuit must be locally ground referenced. The figure shows one way to detect the presence...

A rectifier input capacitor's size is often considered nebulous. Therefore, common practice is to pick a large size, and if the ripple voltage is low enough, all is okay (see the figure, a). If not, it can be increased in size. Other attempts sometimes calculate percent ripple, which I consider a largely useless term because we tend to visualize the waveform as an oscilloscope sees it—a sawtooth waveform with the limit being the...

This design modifies a simple first-order, low-pass filter into a slewing-voltage control that is programmable for its slope and amplitude through a PC's LPT port. These control parameters are typically required for metallurgy studies like corrosion of materials using a potentiostat. (A potentiostat, which is a standalone device, sets the required potential/second for the electrode under corrosion studies.) Figure 1 shows a circuit that supplies...

Single-chip transmitters proposed by some IC manufacturers have good electrical performance, but they're often plagued by some drawbacks. For instance, they're hard to find in small quantities. Also, they become obsolete too fast. And, they rarely have a second source. For frequencies lower than 50 MHz, RF power of 10 mW, and a maximum frequency-shift-keying (FSK) data rate of 2 kbits/s, the circuit shown in the figure can be an attractive solution. The IC used is the...

Many microcontrollers or PICs will have uncommitted digital-to-analog converter (DAC) outputs that can be used to generate sine waves. But these are generally low resolution (8 to 10 bits), yielding a total harmonic distortion (THD) in the 1% range. Or, using a fifth- or seventh-order switched-capacitor filter with a square-wave output ties up two I/O pins on the MCU. One output is used for the filter input and one for the filter clock. Also, the two outputs must be square waves and...

Three electromagnetic interference (EMI) filter arrays with electrostatic discharge (ESD) protection in Thin DFN (TDFN) packages are designed for high-speed LCD display and camera data interfaces with maximum data rates up to 54 Mbits/s per line. Signal components from 800 MHz to 2.9 GHz are attenuated by at least 25 dB. The typical 3-dB point is 110 MHz. All three arrays exhibit extremely low parasitic inductance (10 to 20 pH) due to their TDFN-package ground pads. ON Semiconductor's...