This application note shows how the MAX2170 triple-band (T-DMB, DAB, FM) receiver's input-scattering parameter (S11) is measured for the VHF and L-band inputs.
The MAX2170 direct conversion to low-IF tuner has an input scattering parameter (S11), which is measured for the VHF and L-band inputs. The calibration plane is at the pin of the IC.
The VHF input consists of a bandpass tracking filter followed by an LNA. The return loss will be good for the desired channel, but will look reflective for the out-of-band channels. As a result, the S11 data will change significantly as the MAX2170 tunes to a new channel. To address this issue, the series 91nH inductor, which is part of the VHF tracking filter, was removed from the input for the S11 measurements (Figure 1). Removing this component changes the tracking filter's shape but allows S11 calibration to the pin of the IC. Note, however, that the 91nH inductor is required for the tracking filter to operate properly. It must be used in the final application.
The L-band input consists of ESD diodes and an LNA. The input will look resistive with some shunt capacitance. The S11 data for this input will not vary when the MAX2170 tunes to a new channel. The L-band input can be modeled as a resistor R = 23.4Ω in series with C = 4.2pF.
Table 1 shows S11 data (magnitude and phase) for the VHF and L-band inputs. The RF frequency is changed for each measurement.
|Pin = -50dBm|
Table 2 shows S11 data (real and imaginary) for the VHF and L-band inputs. The RF frequency is changed for each measurement.
|Pin = -50dBm|
The following test files contain S11 data in CITIFILE format for the MAX2170.
|VHF_174.928.d1||VHF input with RF tuned to 174.928MHz|
|VHF_204.64.d1||VHF input with RF tuned to 204.64MHz|
|VHF_239.2.d1||VHF input with RF tuned to 239.2MHz|
|L_5A.d1||L-band input with RF tuned to 1452.96MHz|
|L_9B.d1||L-band input with RF tuned to 1471.792MHz|
|L_13F.d1||L-band input with RF tuned to 1490.624MHz|