FREQUENCY (Hz)

3

0

-3

-6

-9

-12

-15

-18

-21

10k

100k

1M

10M

RFin = 0 dBm

LMH2121

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SNVS876A – AUGUST 2012 – REVISED MARCH 2013

RESPONSE BANDWIDTH

Modulation standards available today have a wide variety of modulation bandwidths. LTE, for instance, has

modulation bandwidths varying from 200 kHz (1RB) up to 20 MHz (100RB). Whether the RF detector can track

the envelope of these modulated RF signals depends on its response bandwidth. Figure 53 depicts the response

bandwidth of the LMH2121. The plot shows the output as a function of a varying amplitude modulation frequency

where the output is normalized to 0 dB at low modulation frequency.

Figure 53. Response Bandwidth

The response bandwidth of the LMH2121 is about 2 MHz for 0 dBm input power level.

SPECIFYING DETECTOR PERFORMANCE

The performance of the LMH2121 can be expressed by a variety of parameters. This section discusses the key

parameters.

Dynamic Range

The LMH2121 is designed to have a predictable and accurate response over a certain input power range. This is

called the dynamic range (DR) of a detector. For determining the dynamic range a couple of different criteria can

be used. The most commonly used ones are:

•

•

The specified dynamic range is the range over which the specified error metric is within a predefined window. An

explanation of these errors is given in the following sections.

Linear Conformance error

The LMH2121 implements a linear detection function. In order to describe how close the transfer is to an ideal

linear function the linear conformance error is used. To calculate the linear conformance error the detector

transfer function can be modeled as a linear function between input power in dBm and output voltage in dBV.

The ideal linear transfer is modeled by 2 parameters:

•

•

and is described by:

(12)

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