7.3.3 Input Frequency Detect

The Log_Out pin creates an envelope proportional to the incoming signal; therefore, the frequency and phase

information of the input signal is lost. The frequency detect feature enables the LOG300 to recover this

frequency information. The frequency detect pin toggles at the same frequency as the input, and can therefore

be used to calculate the input signal frequency or the input signal zero crossing points.

The internal circuit consists of a comparator with one of the inputs connected to the pin Log_In bias voltage and

the other input of the comparator connected to the last stage of the Log Detector gain block (see Figure 7-3).

Log_In is ac coupled; therefore, the incoming signal is biased to the internal bias voltage.

The comparator compares the gained Log_In (both single-ended and differential) signal biased at the internal

bias voltage with the DC internal bias voltage, thereby toggling at every instance of a zero crossing. If the

incoming signal is not a symmetric waveform or consists of multiple frequency content, the frequency detect

feature compares the zero crossings of the incoming signal.

C

1.7k

1.7Vdc

+

–

1.7Vdc

DGND

Freq_Supply

Gain Block 1

Log_Inp

1.7Vdc

Comparator

Freq_Supply

Freq_Out

Log_Out

DGND

Gain Block 2 Gain Block 3 Gain Block N

1.7k

Figure 7-3. Internal Block Diagram for Frequency Detect

7.4 Device Functional Modes

The LOG300 offers three functional modes:

• AFE Disabled

– In this mode, the complete AFE (LOG300) is disabled and consumes only about 100µA.

• LNA Disabled

– In this mode, the LNA is disabled, while the Log Detector block is still operational. See Section 5.6 for

detailed parameters in this mode.

– Typically, this mode is used when the input sensitivity required is relaxed and the application prioritizes a

lower quiescent current. Disabling the LNA helps save 2mA of quiescent current originally consumed by

the LNA.

• Normal operating mode

– In this mode, all blocks of the LOG300 are operational. See Section 5.7 for detailed parameters such as

power consumption, acceptable supply, and input output range.

– This mode can be entered by floating the LNA_En and AFE_En pins or by tying them to VCC.

LOG300

SLOSEB7A – SEPTEMBER 2024 – REVISED OCTOBER 2024

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