1. Overview & Target Audience

️· Device: Micrel QR211HE1 (a receiver/transmitter IC, likely for ISM band applications like 433.92 MHz)
️· Purpose of the Note: Provides application information, including schematic examples, component recommendations, layout considerations, and crystal specifications for using the QR211HE1.
️· Target Audience: Engineers and technicians involved in designing and implementing systems using the QR211HE1.

2. Block Diagram and Key Features

️· Local Oscillator Injection: The QR211HE1 uses *low-side injection*, meaning the local oscillator frequency is *below* the RF carrier frequency. This helps in rejecting unwanted signals.
️· Crystal Frequency Calculation: `F_REF_OSC = F_RF / (32 + 1.1/12)` – Crucial for selecting the correct crystal.
️· Receiver Architecture: The device utilizes an image reject mixer.

3. Application Example & Evaluation Board (QR211HE1):

️· QR211HE1 Example: A starting point is the QR211HE1 evaluation board operating at 433.92MHz. The board has:
- Helical PCB antenna with matching network.
- Band-pass filter front-end.
- Minimum components for operation (crystal, Cagc, Cth capacitors).
️· Antenna Options: The helical antenna's matching network can be removed to use a whip antenna or a direct RF connector connection.
️· Bandpass Filter Front-end: Filters out unwanted noise. Can be omitted if noise isn’t a problem.

4. Component Recommendations & Matching Networks:

️· Matching Network Components (C3 and L2): Used to match the antenna to the IC’s input impedance.
- L2 calculation: Based on the calculated input impedance.
- C3 calculation: Calculated for an input impedance near 50Ω
️· Bandpass Filter Front-End (L1 & C8): Used to reduce unwanted outside band noise.
️· Crystal Selection (Y1/Y1A):
- Load capacitance: 10pF (critical for oscillator operation)
- ESR < 50Ω
- Temperature range: -40°C to +105°C
- See Table 5 for vendor part numbers.

5. PCB Layout Considerations:

️· Crystal Oscillator Sensitivity: The crystal oscillator is very sensitive to stray capacitance.
️· Minimize Stray Capacitance: Avoid long traces and ground planes near the REFOSC pins (RO1 and RO2).
️· Potential Problems:
- Oscillator may take longer to start.
- Time to reliable data on DO pin may be delayed.
- Oscillator might not start at all with high stray capacitance (>20pF).

6. Tables & Key Values


️· Table 2: Matching Values for Helical PCB Antenna (for different frequencies)

Freq (MHz)	C3 (pF)	L2(nH)	Z device (Ω)
390.0	1.5	47	22.5 – j198.5
418.0	1.5	43	21.4 – j186.1
433.92	1.5	39	18.6 – j174.2

️· Table 3: Band-Pass-Filter Front-End Values
- Not explicitly listed; parameters for L1 and C8 needed to calculate resonance frequency.

️· Table 4: Matching Values for most used frequencies

Freq (MHz)	C3 (pF)	L2(nH)	Z device (Ω)
390.0	1.5	47	22.5 – j198.5
418.0	1.5	43	21.4 – j186.1
433.92	1.5	39	18.6 – j174.2

️· Table 5: Crystal Frequency and Vendor Part Numbers

REFOSC (MHz)	Carrier (MHz)	HIB Part Number
12.15269	390.0	SA-12.152690-F-10-H-30-30-X
13.02519	418.0	SA-13.025190-F-10-H-30-30-X
13.52127	433.92	SA-13.521270-F-10-H-30-30-X

In essence, this document provides a practical guide for implementing a 433.92 MHz system using the Micrel QR211HE1, emphasizing component selection, PCB layout, and oscillator operation.