The MAX2640 is a low-cost, low-noise amplifier designed for applications in the 400MHz to 2500MHz frequency range. This application note gives adjustments to the MAX2640 RF matching circuit for 470MHz to 770MHz ISDB-T applications. By optimizing the circuit, it meets the following specifications throughout the operating frequency range: noise figure < 1.2dB, gain > 15dB, input return loss < -3dB, output return loss < -12dB, IIP > -18dBm, input P1dB > -26dBm .

The MAX2640 is a low-cost, low-noise amplifier (LNA) designed for applications in the 400MHz to 2500MHz frequency range. The device operates over a wide voltage range of +2.7 to +5.5V and typically consumes only 3.3mA with low noise figure, high gain, and high input IP3.

Integrated Services Digital Broadcasting (ISDB) is a digital television and broadcast specification for digital broadcast multimedia services in Japan. ISDB-T is the core standard for terrestrial and mobile multimedia applications. In the 470MHz to 770MHz band, ISDB-T divides the 6MHz bandwidth into 13 equal segments. After channel segmentation, different combinations of segments can be used to send programs with different bandwidth requirements (for example, HDTV, SDTV, digital broadcasting, etc.), thereby improving the flexibility of program playback, and the mobile device only occupies 13 segments. One.

Maxim introduces the MAX12160, MAX2161/MAX2162 complete integrated tuners for ISDB-T applications. The MAX2640 LNA can be added to the front end of the ISDB-T tuner with proper tuning to improve the system's noise figure and increase gain. This application note provides matching circuitry to optimize the MAX2640 design for ISDB-T applications.

Optimize LNA indicators

The performance of the RF amplifier can be improved by using appropriate matching components for a specific frequency range. The input and output of the amplifier should be connected to the appropriate signal source and load impedance to ensure efficient signal transmission between the system modules and to minimize the noise introduced by the amplifier to the signal. In general, the optimum noise figure requirements for signal source and load impedance are different from the maximum gain versus signal source and load impedance requirements. In order to optimize the performance of the low noise amplifier, the input and output matching circuits should be adjusted to take into account the noise figure, return loss and gain specifications.

The MAX2640 EV kit helps to quickly evaluate the MAX2640. This application note uses the MAX2640EVKIT to optimize the input and output matching circuitry.

First, to determine the inherent gain and stability of the MAX2640, the MAX2640's VCC pin allows flexible placement of the VCC bypass capacitor to adjust the series inductance of the VCC pin. The series inductance of the VCC pin has a significant effect on the amplifier, introducing an additional parameter that improves performance. Data from previous performance analysis of the MAX2640 show that placing a VCC bypass capacitor approximately 4mm to 5mm from the VCC pin provides a good compromise between inherent gain and stability.

For op amps with poor isolation, the tuning of the output match inevitably affects the input matching circuit. However, due to the high isolation between the output and input of the MAX2640, the input and output matching networks can be individually tuned. In this application note, the output match is first tuned to optimize gain and output return loss.

Second, the input matching circuit should be optimized. The circuit operating bandwidth required by this application note increases the complexity of input tuning. To ensure an ideal flat gain and noise figure over the entire frequency range, appropriate trade-offs should be made. In this application note, it is intended to maintain a constant gain over the entire frequency band and to minimize the noise figure. In order to achieve this goal, the performance of the input return loss has to be sacrificed. The LNA input uses a T-matching network to provide wideband matching; at the same time, a DC blocking capacitor is required at the LNA input.