*Question E7H10:
What information is contained in the lookup table of a direct digital synthesizer (DDS)?*  

*Correct Answer is  B: Amplitude values that represent the desired waveform*  

### AI Response: (may contain errors)  

In a direct digital synthesizer (DDS), the lookup table is a crucial component that stores amplitude values representing the desired waveform. Here's why each choice is correct or incorrect:

1. **Correct Answer: B: Amplitude values that represent the desired waveform**
   - The DDS uses a lookup table to store discrete amplitude values of a waveform, typically a sine wave. These values are used to generate the waveform by converting digital values into an analog signal through a digital-to-analog converter (DAC). This process allows the DDS to produce precise and stable frequencies.

2. **Why the other choices are incorrect:**
   - **A: The phase relationship between a reference oscillator and the output waveform**
     - This choice is incorrect because the lookup table does not store phase relationships. Instead, phase information is managed by the phase accumulator, which determines the current position within the waveform cycle.
   - **C: The phase relationship between a voltage-controlled oscillator and the output waveform**
     - This is incorrect because a DDS does not use a voltage-controlled oscillator (VCO). Instead, it uses a digital phase accumulator and a lookup table to generate waveforms.
   - **D: Frequently used receiver and transmitter frequencies**
     - This choice is incorrect because the lookup table in a DDS is not used to store frequencies. Frequencies are determined by the rate at which the phase accumulator steps through the lookup table.

In summary, the lookup table in a DDS contains amplitude values that are used to construct the desired waveform, making option B the correct answer. The other options describe functions not related to the role of the lookup table in a DDS.