The MAX532 is a dual, 12-bit, voltage-output DAC. Access to the output amplifier's input terminals allows it to be easily configured as a programmable-gain amplifier (PGA) suitable for AC gain control.
The circuit configuraTIon is that of an inverTIng amplifier, with R2 replaced by the effective resistance of the DAC ladder (Figure 1) and R1 replaced by internal feedback resistor RFB (Figure 2). In this circuit, an AC signal is applied to the feedback resistor input and the output signal is tied to the DAC reference input. The maximum signal at VOUT is limited by the amplifier's headroom from the supply rails (± 12V to ± 15V), which must be a minimum of 2.5V from either rail.
Figure 1. Fixed-gain inverting amplifier.
Figure 2. Programmable-gain amplifier.
The DAC functions as a programmable resistor in the feedback of the amplifier such that:
VOUT / VIN = -R (DAC) / RFB,
where R (DAC) is the resistance of the DAC ladder and RFB is the value of the feedback resistor, which is R / 2.
R (DAC) = R / 2 × [4096 / (DAC CODE)], with the DAC CODE given as a decimal value. As the code decreases, the effective DAC resistance increases, and so the gain increases. The transfer function for the circuit is thus:
The code can be programmed between 1 and full scale (212-1). Zero code is not allowed, as it results in the DAC's appearing as an open circuit in the feedback loop.
HDI PCB Specification
High density interconnect (HDI) PCBs represent one of the fastest-growing segments of the printed circuit board market. Because of its higher circuitry density, the HDI PCB design is able to incorporate finer lines and spaces, smaller vias and capture pads, and higher connection pad densities. A high density PCB features blind and buried vias and often contains microvias that are .006 in diameter or even less.
HDI PCBs are characterized by high-density attributes including laser microvias, fine lines and high performance thin materials. This increased density enables more functions per unit area. Higher technology HDI PCBs have multiple layers of copper filled stacked microvias (Advanced HDI PCBs) which creates a structure that enables even more complex interconnections. These very complex structures provide the necessary routing solutions for today's large pin-count chips utilized in mobile devices and other high technology products.
The HDI PCBs we offer include the following highly requested characteristics:
Blind and/or buried vias
Via-in-pad
Through vias from surface to surface
20 µm circuit geometries
30 µm dielectric layers
50 µm laser vias
125 µm bump pitch processing
Applications
HDI PCB is used to reduce size and weight, as well as to enhance electrical performance of the device. HDI PCB is the best alternative to high layer-count and expensive standard laminate or sequentially laminated boards. HDI incorporate blind and buried vias that help to save PCB real estate by allowing features and lines to be designed above or below them without making a connection. Many of today's fine pitch BGA and flip-chip component footprints do not allow for running traces between the BGA pads. Blind and buried vias will only connect layers requiring connections in that area.
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