hf/rf ZONE Products for the week of July 28, 2003
Maxim Integrated Products Says . . .
MAX2055: Low Distortion Differential IF ADC Driver
With Digital Gain Control
Maxim Integrated Products introduced the MAX2055, the industry's first digitally controlled variable-gain amplifier with a differential output to drive high-performance, high-speed analog-to-digital converters (ADCs). The MAX2055 is optimized to deliver IF frequencies from 30MHz to 300MHz. It is ideal for GSM, DCS/PCS, EDGE, iDEN, PHS, cdma2000, and WB-CDMA multicarrier/single carrier base-station applications where high linearity and low noise are required for good bit-error-rate performance.
The highly integrated MAX2055 delivers 23dB of gain range with ±0.2dB
accuracy over the full temperature range. Industry-leading OIP3 performance
is 40dBm over the -3dB to +20dB gain range. When using this device to drive
ADCs, the OIP3 reduces in-band intermodulation noise below that found on
most 12- to 16-bit ADCs. This device integrates a high-performance, digitally
switched attenuator that boasts -12dB of return loss and stable gain performance
over temperature. The on-board fixed-gain amplifier delivers a low 6dB noise
figure, placing the noise level of the MAX2055 significantly below that
of most high-performance 14-bit ADCs. Overall board space used by the DVGA
is 50% less than comparable discrete solutions. With robust reliability
and performance that only silicon-based processes (SiGe) deliver, the MAX2055
beats today's very best GaAs solutions and X-Amp based products.
analogZONE Says . . .
"The industry's first digitally controlled variable-gain amplifier with a differential output to drive high-performance, high-speed analog-to-digital converters." I don't believe that is a valid claim as the AD8370 (an LF to 700-MHz digitally-controlled VGA) was announced some months earlier, on February 24, 2003, and before that the AD8369 would also meet that claim.
Nevertheless, that doesn't mean that the MAX2055 isn't a worthy product. It does a couple of things that the ADI products don't do: It converts a single-ended input into a differential output, a much more likely scenario to have to solve than a differential-input-to-differential-output problem. It also separates the attenuator and the amplifier so that the attenuated RF signal may be filtered off chip before the amplifier section -- and biasing is easier to implement. And Maxim can get away with that and still produce a 5.8 dB noise figure because of the SiGe process they are using. The input return loss shows that the attenuator was put together by a skilled RF designer as the worst case is about 15 dB and can be as high as 30 dB. The output return loss is about 20 dB over the part of the band that will most likely be used -- up to about 150 MHz, and then falls off to about 12 dB at 300 MHz. Logically, too, the amplifier is designed for a 50 O single-ended input and a 50 O differential output.
The MAX2055 offers up to 23 dB of attenuation with a ±0.2 dB accuracy with the amplifier offering a gain of 19.9 dB using a negative feedback system to offer the frequency range and linearity. Gain is set in 1-dB steps using the logic level on five lines to the IC. Current is set with an external resistor and in examples given in the data sheet this can offer a 240 mA consumption with a 40 dBm IP3 at 70 MHz. It is a 5-V part.
External RF chokes are required on the output of the amplifier to provide the dc bias voltage, while another choke is used on the input, also to provide bias.
This is a nice product. The claims the press release makes are an unnecessary diversion from the socket winner that it is. It will find use in cellular and other communications systems on the receive side, it will find applications in test equipment, including industrial ATE, and there will be uses in antenna steering and adaptation as well as low-frequency radar.
The MAX2055 is in production in a thermally-enhanced (grounded, low inductance RF exposed paddle) TSSOP-20 and is priced at $4.95 in 1000-piece lots.