ALM-1412 LNA Module in a GPS Receiver
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Overview of Avago’s ALM-1412 low noise amplifier module, and its implementation in a GPS receiver
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ALM-1412 LNA Module in a GPS Receiver
- 4. Block Diagram FBAR Filter
- 7. GPS Receiver
- 9. Improve Gain and Return Loss The value of L2 was reduced to tune for a better output return loss.
- 10. Single Ended to Differential Conversion RF OUT The value of each components can be calculated by: Discrete Balun
Editor's Notes
- Welcome to the training module on Avago ALM-1412 LNA Module in a GPS Receiver. This training module overviews Avago’s ALM-1412 low noise amplifier module, and its implementation in a GPS receiver.
- Avago Technologies’ ALM-1412 is an LNA module, with integrated filter, designed for GPS band applications at 1.575GHz. The LNA uses Avago Technologies’ proprietary GaAs Enhancement-mode pHEMT process to achieve high gain with very low noise figure and high linearity. Noise figure distribution is very tightly controlled. A CMOS-compatible shutdown pin is included either for turning the LNA on/off, or for current adjustment. The integrated filter utilizes an Avago Technologies’ FBAR filter for exceptional rejection at Cell/PCS-Band frequencies.
- The ALM-1412 is housed in a 12-lead MCOB (multiple-chips-on-board) package with small dimensions, 3.3(L)x2.1(W)x1.1(H) mm 3 . The input pin of the device has a built-in ESD protection circuit which sets the ESD level of the RFin pin to 3kV using the HBM (Human Body Model). The figure shows the simplified internal circuitry. The integrated bias circuitry simplifies external biasing. Unlike typical depletion-mode pHEMT, the enhancement-mode pHEMT LNA that is used in the ALM-1412 only requires one positive voltage supply to bias the LNA. By integrating the FBAR filter, the module achieves excellent out-of-band rejection, and reduces the number of external components and the complexity of the manufacturing process.
- FBAR technology is used to create the essential frequency shaping elements found in modern wireless systems, including filters, duplexers, and resonators for oscillators. This technology produces small size filters with excellent Q. The excellent Q translates into a very steep filter roll-off or superb out-of-band rejection. With the integrated filter, the LNA module achieved exceptional out-of-band rejections, which are 61dBc at the Cell-Band (827.5MHz) and 54dBc at the PCS-band (1885MHz) relative to the GPS frequency (1.575GHz). The excellent out-of-band rejection ensures that the receiver sensitivity is not degraded in the presence of strong interferers.
- The LNA module incorporates a shutdown circuitry that is beneficial for portable devices which have limited battery life. When the module is in shutdown mode, the current consumption is less than 0.1 µ A and the forward isolation is ~17dB. The LNA module can be easily turned off by applying 0V to 0.3V to the Vsd pin (pin 3) which is CMOS-compatible. The Vsd pin can be connected to a microcontroller to switch the LNA module to shutdown mode when it is not needed to extend the battery life.
- A simplified block diagram of a GPS mobile phone receiver is shown in the figure. While the transmitter is sending signal, part of the transmitting signal may leak to the GPS receiver path. Thus, a good rejection to the transmitting signal band (interferer) is required at the GPS receiver path to avoid the GPS chipset from being overloaded by the strong interference power.
- The diagram shows the application circuit schematic of ALM-1412 in GPS receiver application. The input matching of the device is formed by a series inductor to give a very low noise figure of 0.8dB while maintaining a good input return loss. The output matching circuit is formed by L2 and C2 to optimize for the gain and output return loss. The gain will increase with a higher value of C2 but this will degrade the stability. The input third order intercept point of the circuit can be improved by increasing the value of L2 but at the expenses of poor output return loss. Resistor R1 helps to improve the stability of the circuit, a resistor value of less than 6.8 ohm may make the circuit potentially unstable. C1, C2 and C3 are bypass capacitors. C9 is a DC blocking capacitors but it is not needed in the actual application because there are blocking capacitors integrated internally at both the input and output of the device. All of the 3 components C1, C3 and C9 are optional in the actual application. Essentially, the external components needed in the actual application are as low as four matching/stability components (L2, L3, C2, and R1) and one bias resistor (R2).
- The gain of the LNA module can be improved by matched the device’s input and output closer to 50 ohm. A series inductor followed by a shunt inductor topology is required to get to this impedance. The value of L2 at the device’s output was reduced to tune for a better output return loss. This modification will improve both the input and output return loss to more than 10 dB. The gain is 0.7dB higher while still maintain a low noise figure of 1 dB. The rejection at PCS-band is improved to 59 dBc but the IIP3 is slightly degraded to 5 dBm. The figure shows the circuit’s schematic.
- This diagram shows the simplified block diagram for the front end of GPS receiver. The single ended amplifier’s output need to be converted to a differential output while the module is integrated to the system with a differential input device as next stage (example: differential input mixer to down convert the signal’s frequency). This can be achieved by using a balun transformer or a discrete balun. For applications which need good performance over narrow bandwidth, a discrete balun offers low cost solution.
- Thank you for taking the time to view this presentation on ALM-1412 LNA Module in a GPS Receiver . If you would like to learn more or go on to purchase some of these devices, you may either click on the part list link, or simply call our sales hotline. For more technical information you may either visit the AVAGO TECHNOLOGIES site – link shown – or if you would prefer to speak to someone live, please call our hotline number, or even use our ‘live chat’ online facility.