Datasheet LTM9004 (Analog Devices) - 14

LTM9004
operaTion DESCRIPTION
VCC1 VCC2 VCC3 VDD The LTM9004 is a direct conversion receiver targeting OV high linearity receiver applications, such as wireless DD infrastructure with RF input frequencies up to 2.7GHz. RF 1ST 2ND LPF ADC AMP AMP It is an integrated μModule receiver utilizing system in a MIXER OGND package (SiP) technology to combine a dual, high speed 9004 F02 GND 14-bit A/D converter, lowpass filters, two low noise dif- LO OFFSET ADJ ADC CLK ferential amplifiers per channel with fixed gain, and an I/Q
Figure 2. Basic Functional Elements (Only Half Shown)
demodulator with DC offset adjustment. The direct conversion receiver architecture offers several
SEMI-CUSTOM OPTIONS
advantages over the traditional superheterodyne. It eases The μModule construction affords a new level of flexibility the requirements for RF front-end bandpass filtering, as it in application-specific standard products. Standard ADC, is not susceptible to signals at the image frequency. The amplifier and RF components can be integrated regardless RF bandpass filters need only attenuate strong out-of-band of their process technology and matched with passive signals to prevent them from overloading the front end. components to a particular application. The LTM9004-AA, Also, direct conversion eliminates the need for IF ampli- as the first example, is configured with a dual 14-bit ADC fiers and bandpass filters. Instead, the RF input signal is sampling at rates up to 125Msps. The amplifiers provide a directly converted to baseband. total voltage gain of 14dB (including the gain of the mixer). Direct conversion does, however, come with its own set The lowpass filter limits the bandwidth to 1.92MHz. The of implementation issues. Since the receive LO signal is at RF and LO inputs of the I/Q demodulator have integrated the same frequency as the RF signal, it can easily radiate transformers and present 50Ω single-ended inputs. An from the receive antenna and violate regulatory standards. external DAC can be used for DC offset cancellation. Unwanted baseband signals can also be generated by 2nd However, other options are possible through Linear order nonlinearity of the receiver. A tone at any frequency Technology’s semi-custom development program. Linear entering the receiver will give rise to a DC offset in the Technology has in place a program to deliver other sample baseband circuits. The 2nd order nonlinearity of the receiver rate, resolution, gain and filter configurations for nearly also allows a modulated signal, even the desired signal, any specified application. These semi-custom designs to generate a pseudo-random block of energy centered are based on existing components with an appropriately about DC. modified passive network. The final subsystem is then For this reason, the LTM9004 provides for DC offset cor- tested to the exact parameters defined for the application. rection immediately following the I/Q demodulator stage. The final result is a fully integrated, accurately tested and Once generated, straightforward elimination of DC offset optimized solution in the same package. For more details becomes very problematic. Necessary gain in the baseband on the semi-custom receiver subsystem program, contact amplifiers increases the offset because their frequency Linear Technology. response extends to DC.
MIXER OPERATION
The following sections describe in further detail the opera- tion of each section. The μModule technology allows the The RF signal is applied to the inputs of the RF trans- LTM9004 to be customized and this is described in the conductance amplifiers and is then demodulated into I/Q first section. The outline of the remaining sections follows baseband signals using quadrature LO signals which are the basic functional elements as shown in Figure 2. internally generated from an external LO source by preci- sion 90° phase shifters. 9004fa 14 For more information www.linear.com/LTM9004 Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Dynamic Accuracy Converter Characteristics Digital Inputs and Outputs Power Requirements Timing Characteristics Timing Diagrams Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Package Description Revision History Typical Application Related Parts