RF System Design for Communications – Lecture 12 – Direct-conversion receiver, its disadvantages, I/Q mismatch

Lecture 12 – Direct-conversion receiver, its disadvantages, I/Q mismatch

Haberleşme için RF Sistem Tasarımı – Direct conversion alıcı, dezavantajları, I/Q mismatch

Notice: The digital notes were created from the handwritten notes with the help of Claude (Anthropic); they are meant as a supplementary resource and may contain errors. Always rely on the original notes and the official course materials.

What is in this note?

Section headings of the note (in Turkish):

Direct Conversion Receiver

Drawbacks of Direct Conversion Receivers

(1) LO Leakage

(2) DC offset

Solving DC Offset

(3) Even Order Distorsion

(4) Flicker noise

Flicker noise Penalty

I/Q Mismatch (Drawbacks of Quadrature Downconversion)

Outputs

Only gain mismatch (θ = 0)

Only phase mismatch (ε = 0)

Solutions of I/Q Mismatch

Text of the note

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Direct Conversion Receiver

→ One step Conversion

Simple design process

Mixing spurs are reduced

FSK Direct Conversion Receiver

Anlamak için 2 bit gönderdiğimizi düşünelim

Şimdi bunları bir demodülatöre sokuyoruz

Drawbacks of Direct Conversion Receivers

To minimize LO leakage

Symmetric layout for Oscillator

DC offsetten kurtulmalıyız

LO leakage at the input of LNA is -60 dBm

Solving DC Offset

modulation index (FSK)

Bunun başka dezavantajı var

Drawback of Direct conversion Receivers

(3) Even Order Distorsion

Mixer layout should be symmetrical

We ignore noise effect below f_BW1000 since they vary slowly

Flicker noise Penalty

Flicker noise penalty

→ normalde f_c ana bant bitiyor formülü uygularken dikkat edin

I/Q Mismatch (Drawbacks of Quadrature Downconversion)

Phase & gain Error

Only phase mismatch ( ε = 0 )

Bunu çözmek için ne yapmak gerekiyor

Solutions of I/Q Mismatch